Diagnosing and Maintaining

Your Commodore 64
or 128 Sytstem
Diagnosing and Maintaining
Your Commodore 64
or 128 System
CHRIS MORRISON AND
TERESA S. STOVER
 Commodore 64, Commodore 128, VIC 1541, VIC 1571 VIC Datasette. and VIC·
MODEM are trademarks of Commodore Business Machines. Inc
CompuServe IS a registered trademark of CompuServe Consumer Information
Service
CP/M IS a registered trademark of Digital Research Inc.
Dow Jones News/Retrieval is a registered trademark of Dow Jones & Company.
Inc
Smartmodem IS a trademark of Hayes Microcomputer Products. Inc
The Source is a trademark of Source Telecomputmg Corporation
VT100 IS a trademark of Digital Equ,pment Corporation

TAB ~OOKS Inc. offers software for

sale. For information and a cataiog.
pleasE' contact TAS Software
Department. Blue Ridge Summit.
Pl\ 17294-0850.

FIRST EDITION
FIRST PRINTING

Copyright 1988 by TAB BOOKS Inc.

Printed In the United States of America

Reproduction or publication of the content in any manner. without express

permission of the publisher, is prohibited. No liability is assumed with respect to
the use of the information herein.

Library of Congress Cataloging in Publication Data

Morrison, Chris.
Commodore care manual. diagnosing and maintaining your 64 or 128
system / by ChriS Morrison and Teresa S Stover.
p. cm.
Includes Index.
ISBN 0-8306·3141-0 (pbk.)
1. Microcomputers-Maintenance and repair. 2. Commodore 64
(Computer) 3. Commodore 128 (Computer) I. Stover, Teresa S.
II. Title.
TK887.M65 1988 88·4925
621.391 '6~dc19 CIP

Questions regarding the content of this book

should be addressed to:

Reader Inquiry Branch

TAB BOOKS Inc.
Blue Ridge Summit, PA 17294·0214
 Pr.gra. Lis.
The System Diagnostic Main Menu Module 9
The System Diagnostic Utility Subroutines 12
The Keyboard Diagnostic Module 39
The Monitor Diagnostic Module 64
The Printer Diagnostic Module 89
The Cassette Drive Diagnostic Module 108
The Disk Drive Diagnostic Module 133
The Serial Communication Diagnostic Module 150
The System Exerciser Module 156
The Joystick Diagnostic Module 172
Commodore 64 System Diagnostic Program 176
Commodore 128 System Diagnostic Program 187
Acknowledg_enls
The following individuals helped bring about the successful completion of this
book, and for that we would like to express our hearty appreciation.

Craig A. Stover edited the manuscript, shot the photographs, provided mor-
al support, and acted as our public relations representative through his incessant
bragging about us.

Pat A. Mahony edited the manuscript, gave us encouragement and inspiration,

and always made us feel like we were doing something worth doing.

Diana H. Price edited the manuscript, and offered us her unique blend of
humor, sympathy, and food while having to work with the authors.

IIva Klar created the manual line drawings and loaned us her Commodore
64 system for research and development of this book and the software.

We would especially like to thank Qubix Graphic Systems, Inc. for allowing
Chris to create the electronic line drawings of the Qubix Designer Workstation.
 Conlellis
Introduction xiii
Preventive Maintenance
Repair Guidelines
Diagnostics
Exerciser
Creating Your Own Diagnostics

I Getting Started
System Overview
1

The System Unit

The Keyboard
The Monitor
The Printer
The Cassette and Disk Drives
The Serial Communication Interface
The System Diagnostic Program 4
System Diagnostic Program Summary
Running the System Diagnostic Program
 How the Main Menu Module Works
The System Diagnostic Program Utility 12
Subroutines 12
Program Modification and Adaptation
Tools and Resources
Documentation
Tools
Spares
User Resources
Troubleshooting and Repair Guidelines 21
Limits/Tinkering 21
Maintenance and Techniques 22
General System Care
Preventive Maintenance
Troubleshooting Techniques
What To Do First 25

The System Unit/Keyboard 27

Description and Function of the System Unit 27
Description and Function of the Keyboard 28
How the Keyboard Functions
Troubleshooting and Repair Guidelines 29
PROBLEMS:
The Keyboard Doesn't Work At All
Particular Keys Do Not Work
Keys Stick When Pressed
A Key Doesn't "Feel" Right
Running the Keyboard Diagnostic Module 34
How the Keyboard Module Works 38

The Monitor
I Description and Function of the Monitor 46
46

Types of Monitors
How the Monitor Functions
Troubleshooting and Repair Guidelines 51
PROBLEMS:
Nothing Displays on the Monitor
Static on the Television Screen
Etching
Blank Character Location
Misaligned Display
A Particular Character Does Not Display
Colors Do Not Display Correctly
Sprites Do Not Display Correctly
Running the Monitor Diagnostic Module 58
 Display Test
Alignment Test
Character Set Test
Color Test
Scroll Test
Sprite Test
How the Monitor Module Works 62

GL The Printer 76
--- Description and Function of the Printer 76
Types of Printers
Printer Interfaces
Troubleshooting and Repair Guidelines 79
PROblEMS:
The Printer Does Not Work
Poor Print Quality
A Horizontal Tab Is Not Working
Paper Does Not Feed Properly
Certain Characters Do Not Print
Certain Characters 00 Not Print Completely
Installing a New Printer
Running the Printer Diagnostic Module 84
Sliding Alpha Test
Display Character Print Test
Echo Character Print Test
HOrizontal Tab Test
Line Feed Test
How the Printer Module Works 88

I The Cassette Drive

Description and Function of the Cassette Drive 99
98

How the Cassette Drive Functions

The Cassette Tape Media
The Cassette Tape Drive
Troubleshooting and Repair Guidelines 102
PROBLEMS
The Cassette Drive Does Not Work
Drive Is Not Reading or Writing Correctly
Running the Cassette Drive Diagnostic Module 106
How the Cassette Drive Module Works 107

The Disk Drive 113

Description and Function of the Disk Drive 113
Types of Disk Drives
How a Disk Drive Functions
 Troubleshooting and Repair Guidelines I 19
PROBLEMS:
The Disk Drive Does Not Work
Cannot Read or Write to the Diskette
Cannot Load a Program or Read a Data File
Head Crash
Read Data Is Garbled
20 Read Error
21 Read Error
23 Read Error
24 Read Error
25 Read Error
26 Write Protect On
27 Read Error
28 Write Error
62 File Not Found
66 Illegal Track and Sector
74 Drive Not Ready
Preventive Maintenance 130
Running the Disk Drive Diagnostic Module 130
How the Disk Drive Module Works 132

7 The Serial Communication Interface

Description and Function of the Serial
137

Communication Interface 137

Types of Serial Communication Devices
How the Serial Communication
Interface Functions
Troubleshooting and Repair Guidelines 144
PROBLEMS:
Communication Cannot Be Established
Communication Results Are Garbled
Printer Does Not Work
Running the Serial Communication Interface
Diagnostic Module 147
How the Module Works 149

• Post-Repair Test and Burn-In

Function of the Exerciser 153
Running the System Exerciser 154
How the System Exerciser Module Works 155
152

161
9 Writing Diagnostics for Other Peripherals
Types of Microcomputer Peripherals 162
 Developing a New Diagnostic Module 162
Learn the Functions of the Device
Read the Device Manual
Decide What to Test For
Create a Program Flowchart
Write the Diagnostic Module
Integrate the New Module
Test the New Diagnostic Module
Developing the Joystick Diagnostic Module 165
Functions of the Joystick
Information about the Joystick
Troubleshooting and Repair Guidelines 167
PROBLE.~1S
Joystick Does Not Work At All
Joystick Does Not Work In a Particular
Direction
Fire Button Does Not Work
Joystick Tests
The Joystick Module Flowchart
Writing the Joystick Diagnostic Module
Integrating the Joystick Module
Testing the Joystick Module

Appendix A Commodore 64 System Diagnostic

Program listing 176
Appendix B Commodore 128 System Diagnostic
Program listing 187

Appendix C Commodore 128 BASIC Programming 198

Index 202
 Introduction
The computer is perhaps among the most revolutionary inventions in our history.
Its presence infl uences our culture and each of our lives in many ways. Particular
prominence belongs to the microcomputer, known as the "personal computer."
You might use a personal computer such as the Commodore 64 or Commodore
128 to help manage a small business, to do schoolwork, to plan the home budget,
to keep records, to write, or even to play games. Knowledge of computer software
applications, however, is not necessarily accompanied by knowledge of the
computer hardware and its functions.
Being a machine, the computer can malfunction and break down, just like
any other device or appliance you might use. If you've had your computer for
a while, and it's beginning to show signs of age and wear, you might have already
experienced trips to a computer service center, with their disheartening repair
bills. Although you are not a computer technician, and you do not know dc and
ac electronics, you do feel you are capable of having more control over the care
of your computer-saving yourself time and money.
This book helps you attain that goal. You need no previous experience with
computer programming or repair for this book to be useful to you. All you need
is a conscientious desire to take better care of your Commodore and to diagnose
problems as they emerge.
This book provides you with three basic approaches to Commodore care:
preventive maintenance, diagnostics when something goes wrong, and general
repair once you discover the source of the problem.

xiii
xiv

These methods and procedures will help you better understand the internal
workings of your system, enabling you to maintain a well-running system less
likely to experience long periods of "downtime." You will save time from not
having to deal with a broken computer, and save money from fewer trips to the
computer service center. You might also gain a new understanding of BASIC pro-
gramming. You will certainly gain more control from knowledge about your
computer.

PREVENTIVE MAINTENANCE
To avoid breakdowns and their associated troubles, certain preventive
measures are necessary. Following these procedures will help you maintain your
computer in its best possible condition.
Chapter 1 outlines general practices that help keep your Commodore healthy.
It also explains periodic preventive maintenance procedures that can stave off
system problems. Troubleshooting techniques are explained to help you isolate
problems.
Each succeeding chapter specializes in a particular Commodore subsystem:
the system unit, the keyboard, the monitor, the printer, the cassette tape drive,
the disk drive, and the serial communication interface. Each of these subsystem
chapters provides a brief theory of operation, a I ist of possible problems with
troubleshooting and repair techniques, and an explanation of the associated
diagnostic program module.

REPAIR GUIDELINES
If you suspect a problem with some part of your computer system, refer to
the appropriate subsystem chapter. Within that chapter, refer to the
"Troubleshooting and Repair Guidelines" section. Then look up the problem that
fits what your system is experiencing. Follow the troubleshooting and repair
instructions in the order given. This becomes the computer's "treatment plan."
By following these instructions, you can often fix the problem yourself. If it's
a more complex problem, you can take the system to a computer service center
with a more educated in-depth explanation, a diagnosis of the problem, and a
specific directive of what must be done. This saves the technician repair time,
thereby saving you money.

DIAGNOSTICS
In addition to the "Troubleshooting and Repair Guidelines," the "System
Diagnostic Program" can assist with the troubleshooting task. This BASIC program
includes seven modules, each designed to perform a series of tests on a different
component. You can buy the program on a diskette (refer to the last page of this
book), or you can key it in yourself, because complete program listings for both
the Commodore 64 and the Commodore 128 are provided in the appendices.
The System Diagnostic Program lets you gather information in order to
determine whether the subsystem being tested has a problem, and to pinpoint
where that problem lies. The "Troubleshooting and Repair Guidelines" indicate
 xv

when a particular test should be performed. Instructions for running the module
are provided in their own section, along with illustrations of expected test results.
After executing these tests, you'll be able to make a diagnosis and take the
appropriate action.
The program listings and detailed line-by-line explanations of this program
"code" are also included in the corresponding chapters. This is particularly useful
if you know how to program in BASIC, and would like to understand the workings
and logic of the programs. This can also help you modify the program for your
own purposes or for creating new modules for additional subsystems and
peri pherals.
In these line-by-line explanations, the code for the Commodore 64 is used
as a model. The code for the C64 and C128 are similar, but not identical. When-
ever there is a difference between the two, this is noted within the text. In addition,
Appendix C summarizes the major programming differences between the two
systems.
The program listings provided throughout this book use a particular
convention. When a special symbol representing a special key or program output
is part of an instruction, { } braces enclose the word describing the symbol. For
example, consider the following instruction:

PRINT" {CLR/HOME}":RETURN
The words CLR/HOME are not actually in the instruction; rather, the CLR/HOME
key is pressed as part of the instruction. The words are simply spelled out in these
listings for your clarification.
Another example of this is found in the Color Test of the Monitor Diagnostic
Module:

PRINT" {CTRL 1} Black" TAB(12)C$

Here, the words in braces, CTRL 1, are the keys that are pressed in order to change
the color to black.
If you are not familiar with BASIC, you can easily skip the program explanations
and still use the diagnostic modules successfully. The entire program is ready to
use. Just create a backup of the program, then load it into your system.

EXERCISER
After you have your computer repaired, you will want to make sure that the
problem has really been solved. The computer is a system of many components,
and as such, when something goes wrong in one part of the computer, it could
actually be caused by something in another part. The Exerciser Module of the
System Diagnostic Program lets you make sure that the system as a whole is work-
ing properly. This is described in Chapter 8.
When you run the Exerciser Module after having a problem repaired, all
system functions are exercised and run for a period of time. This is much like
test-driving your car after repair. The program "burns-in" and tests the system
to confirm that it works correctly and to ensure that there are no recurring
problems.
xvi

CREATING YOUR OWN DIAGNOSTICS

If you know BASIC programming, this book provides you with the techniques
necessary to develop new diagnostic routines for peripherals not covered in this
book. Suppose you have another peripheral such as a digitizer tablet or a joystick,
for which you want to develop a diagnostic program. The information in this book
presents a systematic diagnostic approach that will help you learn how to predict
the problems that can occur with that equipment.
Once you learn the types of problems that can occur, and you have the
information needed to diagnose these problems, you can write a program or add
a new routine appropriate to such a troubleshooting activity. Chapter 9 discusses
this in detai I.
In every case, we have done our best to ensure the accuracy and reliability
of the information presented in this book. However, we cannot guarantee that
your computer will behave as expected, nor can we be responsible for any
malfunctions or damages that occur as a result of following the suggestions in
this book. Nonetheless, the diagnostics and instructions should be sufficient to
help you pinpoint problems when they arise.
 Chapter 1
Gelling
Slarle.
This chapter helps you to better understand your Commodore system, to use the
System Diagnostic Program to troubleshoot problems, and to get these problems
fixed through troubleshooting and repair procedures.
Fi rst, the Commodore system with its standard components and peripherals
are described. Next, the System Diagnostic Program is discussed, along with a
summary of the individual modules. Resources and tools necessary for
troubleshooting and repairing Commodore malfunctions are listed. In addition,
a section on general maintenance and troubleshooting techniques is included to
provide a good foundation for computer care.

SYSTEM OVERVIEW
The typical Commodore computer system consists of the following
components:
o system unit
o keyboard
o monitor
o printer
o cassette drive and/or disk drive(s)
o serial communication interface

You might have more peripherals on your particular system, but this is a basic
configuration, resembling the system shown in Fig. 1-1.
2 Getting Started

Fig. 1-1 . Basic Commodore configuration

Although the components are covered in more detail in their individual

chapters, a brief description of each is provided here. This general overview
describes how the various components interact to perform the work expected of
a computer system.

The System Unit

The system unit is the actual computer. On the Commodore systems, the
system unit is housed in the same assembly as the keyboard . The system unit
is the "brains" of the computer, and as such, is the single most important
component of the computer.
The system unit houses the central processing unit (CPU), as well as the various
interfaces for the computer's peri pherals. The CPU consists of the microprocessor
chip that runs the computer. It issues commands that cause calculations to be
made and processes to be run. The CPU coordinates the various input and output
devices. It transfers and processes data to and from the outside world.
The Commodore 64 system unit consists of the 6510 CPU chip with 64
kilobytes of memory. It also includes the disk drive controller, serial
communication interface, serial printer interface, cassette interface, and monitor
interface.
The system unit for the Commodore 128 includes the 6502/ 8502 CPU chips,
a Z80 processor for running CP/M, 128 kilobytes of memory, a disk controller,
 Commodore Care Manual 3

serial communication interface, serial printer interface, cassette interface, and mon-
itor interface. Just like the Commodore 64, the 128 system unit is housed in the
same unit as the keyboard. Further information about the system unit is found
in Chapter 2.

The Keyboard
The keyboard is the Commodore's primary input device from the outside
world. Typed characters form commands, move the cursor, and enter data. The
keyboard receives the code of the characters entered, sends them to the system
unit for processing and interpretation, and displays the appropriate results on the
monitor screen. Further information about the keyboard is provided in Chapter 2.

The Monitor
The monitor is the visual output for work done on the Commodore. It is also
known as a cathode ray tube (CRT) or video display. The monitor is the output
device that shows your input data from the keyboard, modem, joystick, or other
input device. It also displays the result of system processing performed within
the system unit. The Commodore usually uses a color monitor, and this can be
either a standard television set or a computer monitor. Further information about
the monitor is found in Chapter 3.

The Printer
Like the monitor, the printer is an output device. However, while the moni-
tor provides output on the screen, the printer provides output on paper, or
hardcopy. A serial interface connection between the system unit and the printer
causes data and processing results to be transferred from the system to the print-
er. You might have a dot-matrix or letter-quality printer. Learn more about the
printer in Chapter 4.

The Cassette and Disk Drives

Both the cassette drive and disk drive are used to store and recall software
programs and data by magnetically recording and recalling electronic bits. The
cassette tape drive uses regular audio cassette tapes for storage, while the disk
drive uses floppy diskettes as the storage media. Chapter 5 discusses the cassette
drive in greater detail, and Chapter 6 does the same for the disk drive.

The Serial Communication Interface

The serial communication interface is the means for your Commodore to
"talk" to the outside world. It can connect to, or interface with, a modem, which
sends data to and receives data from another computer over telephone lines. It
can interface with a printer, transmitting data to be printed. It can also interface
directly with another computer. For further information about the serial
communication interface, refer to Chapter 7.
4 Getting Started

THE SYSTEM DIAGNOSTIC PROGRAM

The System Diagnostic Program is divided into several modules. Each module
includes the necessary program instructions for exercising a particular device on
your Commodore and testing for possible problems. The devices that can be tested
with this program are those of a typical configuration: keyboard, monitor, cassette
drive, disk drive, printer, and serial communication interface.

System Diagnostic Program Summary

The block diagram in Fig. 1-2 outlines the structure of the System Diagnostic
Program. As you can see, lines 5 -35 are set aside for explanation remarks as
well as for the storage of any constants and variables that are used throughout
the program. The numbers within each of the blocks are the line numbers where
the code for that subsystem module is located.
The first module is the System Diagnostic Main Menu. The program code
for the Main Menu Module, residing in lines 50-180, is described later in this
chapter. The code for the other modules is listed and explained in the appropriate
subsystem chapter. For example, the code for the Monitor Diagnostic Module
is explained in Chapter 3, "The Monitor."
The second module in the program is the Keyboard Diagnostic Module. This
module runs a test which echoes and gives the numeric code, or CHR$ code
value, of any key you press. If you press a function key, the function key name
and/or combination is displayed on the screen. The Keyboard Diagnostic Module
resides in lines 200-740.
The third module is the Monitor Diagnostic Module. This module consists
of six different tests residing in lines 800-1930:

D The Display Test fills the entire screen with a specified character. This lets
you check that each location on the monitor is capable of displaying data.
D The Alignment Test displays a series of vertical and horizontal lines to let you
check that the monitor is properly aligned.
D The Character Set Test displays your monitor's full set of available display and
graphic characters.
D The Scroll Test provides a sl idi ng character set to let you check that the moni-
tor is scrolling correctly.
D The Color Test checks the 16 available colors with a color pallet test.
D The Sprite Test checks the special circuitry used to display and move sprites,
which are used in many Commodore game applications.

The Printer Diagnostic Module is stored at lines 3500-4150. It is made up

of five tests:

D The Sliding Alpha Test lets you check each letter of the printer's available
character set.
D The Display Character Print Test displays the primary character set that the
pri nter recogn izes.
 Commodore Care Manual 5

Constant. and
V.rlables
Unes 6-36

1
Main Menu Module
Unes 60-180

!
Keyboard Diagnostic
Module
Lln.s 200-740

!
Monitor Diagnostic
Modul.
Unea 800-11130

!
Printer DI.~nostlc
Modu.
Une.3600-4160

1
C....n. Diagnostic
Fig. 1-2. System Diagnostic Program block diagram. Module
Un.s 4200-4800

T
Disk Drlv. D I.g nostlc
Module
Unes 6000-6200

!
Serial Comm
DI.gnostlc Modul.
Unes 6000-6110

1
Joystick Diagnostic
Module
Unes 7000-7130

1
Exercl ..r Diagnostic
Modul.
Un•• 7200-7470

1
Addltlon.1 Modules
Une. 7600-64000
6 Getting Started

o The Echo Character Print Test lets you check whether or not a particular
character can be pri nted.
o The Horizontal Tab Test checks all horizontal tab positions.
II The Line Feed Test checks various line space gradations, including the feeding
of a new continuous form page.

The Cassette Drive Diagnostic Module tests and exercises the two main
functions of a cassette drive: reading and writing to the cassette. This module is
found at lines 4200-4600.
Likewise, the Disk Drive Diagnostic Module tests and exercises the two main
functions of a disk drive: reading and writing to the diskette. This test supports
both the 1541 and 1571 floppy disk drive models. Lines 5000-5200 contain this
disk drive test.
Lines 6000-6110 contain the Serial Communication Diagnostic Module,
which lets you test the serial communication interface. For this test, you press
a key on the keyboard, and the character is echoed on the screen. This "Ioopback"
test determines whether or not the modem interface is functioning.
The Joystick Diagnostic Module, located at lines 7000 through 7130, is the
example used in Chapter 9 to demonstrate how you could go about developing
and integrating your own diagnostic module for any additional peripherals you
might have.
The final program module is the System Exerciser Module at lines 7200 to
7470. If you have just purchased a new Commodore, or if you've just brought
your computer back from servicing, it's a good idea to burn-in the system. Burn-
in is a continuous testing mode that exercises all system functions. This is
particularly useful when the computer is first set up, or when it is moved, because
that is when most problems take place. The Exerciser Module allows you to burn-in
and check system functions automatically and unattended.
Five system utility subroutines are included at lines 2990 through 3300. These
subroutines include the Clear Screen subroutine, the Get-a-Key subroutine, the
Beep subroutine, the Key-to-End-Test subroutine, and the Key-to-Continue
subroutine. These subroutines are explained later in this chapter.

Running the System Diagnostic Program

If you have purchased the diskette containing the System Diagnostic Program
(refer to the back page of this book for more information), the first thing you need
to do, as with any new program diskette, is make a backup copy and keep the
original in a safe place.
If you have not purchased the diskette, access BASIC on your system, and type
in the appropriate version of the code as listed in the appendices. Appendix A
provides the Commodore 64 program listing, and Appendix B provides the
Commodore 128 version.
Try out each program function and make sure there are no syntax errors which
would indicate typographical errors made while entering the program.
After keying the program in, be sure to save the program on your disk or tape,
and make another backup copy of it.
 Commodore Care Manual 7

NOTE: It is imperative that you key the program in before you have a system
problem. If you wait until after you suspect a malfunction, you might not
be able to enter the program for some reason attributed to this malfunction.
Even if you are able to enter and run the program, your test results might
be inaccurate and misleading.

From a Disk Drive. To run the diagnostic on your disk drive, follow these steps:

1. Boot up the system. BASIC is loaded automatically, and the OK prompt is

displayed.
2. Place the diagnostic diskette into the disk drive.
3. Enter LOAD" diag" ,8. The System Diagnostic program is loaded into BASIC.
4. Enter RUN.

From a Cassette Drive. To run the diagnostic from a cassette tape drive, follow
these steps:

1. Boot up the system. BASIC is loaded automatically, and the OK prompt is

displayed.
2. Insert the cassette with the diagnostic program into the cassette drive.
3. Enter LOAD" diag". (The file name "diag" is simply the name we've given
the System Diagnostic Program. Of course, you can name it whatever you
like when you're entering the program yourself, or you can change the file
name later.) The System Diagnostic Program is loaded into BASIC, and the
OK prompt is displayed.
4. Enter RUN.

Once the program is loaded, the screen displays the System Diagnostic Main
Menu. This menu allows you to choose from several diagnostic options, as shown
in Fig. 1-3.
A selection is made by pressing the one-character command which is the first
letter of the name of the desired test. For example, if you wish to run the keyboard
test, enter K or k. The program is not character case-sensitive.
When you press a valid selection, the screen is cleared and you are either
presented with a new menu, or the desired test begins immediately. If you enter
an inval id command, such as Z or R, the system beeps and returns to the selection
mode to let you try again.
When you press Q, the program "quits," or ceases operation, and returns
you to the BASIC environment.

How the Main Menu Module Works

Now that you are familiar with the general structure of the Main Menu Module,
you can begin to understand how the program works, line by line. A listing of
the Main Menu Module is found in Fig. 1-4.
8 Getting Started

System Diagnostic

<K>eyboard Test <S>erial Comm Test

<M>onitor Test <D>isk Drive Test
<C>assette Test <J>oystick Test
<P>rinter Test <E>xerciser
<Q>uit

Enter Selection

Fig. 1-3. The System Diagnostic Main Menu.

Remember, you can skip this section if you are not familiar with BASIC pro-
gramming, or if you are not interested in how the program works. Skipping this
section and the uihers like it throughout the book \\':1! r:ot in .1::1' v\'ay d!!T!!ni~h
your ability to use the System Diagnostic Program to troubleshoot and repai r your
Commodore.
Line 1 indicates the version of the code-Commodore 64 or Commodore 128:

REM "Commodore 64"

Line 5 indicates the title and copyright of the System Diagnostic Program:

5 REM "System Diagnostic Program Copyright 1988 TAB BOOKS Inc."

Line 10 uses the POKE statement to set the graphic character mode to be used
in the test. Then an array is established for a keyboard map by using a DIMENSION
statement to initialize variable K$ to 63:

10 POKE 53272,23:DIM K$ (63) :REM Set Character Set

C128 USERS: In the C128 code, the POKE and DIM K$ statements are
modified to accommodate the larger keyboard.

Lines 20 through 24 contain DATA statements. This series of DATA statements

 Commodore Care Manual 9

REM "Commodore 64"

5 REM "System Diagnostic Program Copyright 1988
TAB BOOKS Inc."
10 POKE 53272,23:DIM K$(63):REM Set Character Set
20 DATA "INST/DEL","RETURN","CRSR RT","F7","F1","F3","F6",
"CRSR UP","3","I0/","A"
21 DATA 114 11 ,IIZ",IISII,IIEII,1I ",IIS","rll,IIOII,1I6",IICII,IIFII,
"TII,IIXIl,1I711,IIY","GII,1I8 11 ,1I8"
22 DATA IIHII,IIU",IIVII,1I9 11 ,III",IIJ","OII,IIM","K",IIO",IINII,
"+II,lIpn,IILII,II_II,II.II,II:",II@1I

23 DATA ",",II£II,II*II,II;II,IICLR/HOMEII," ",II=",lIfll,II/",1I1 11 ,

11_11,11 ",1I211,IISPACEII
24 DATA" ","Q"
25 FOR I =0 TO 62: READ K$( I): NEXT
30 DIM R(8):DATA 1,2,4,8,16,32,64,128
35 FOR 1=0 TO 7:READ R(I):NEXT
50 GOSUB 2990: PRINT TAB(12) "System Diagnostic":PRINT:
60 PRINT TAB(3) "<K>eyboard Text <S>erial Comm Test"
70 PRINT TAB(3) "<M>onitor Test <D>isk Drive Test":
80 PRINT TAB(3) "<C>assette Test <J>oystick Test":
85 PRINT TAB(3) "<P>rinter Test <E>xerciser":
90 PRINT TAB(16) "<Q>uit":PRINT:PRINT TAB(12)
"Enter Selection"
100 GOSUB 3000:REM Get Key Command
110 IF A$="K OR A$="k" THEN 200
120 IF A$="M OR A$="m" THEN 800
130 I F A$="P OR A$="p" THEN 3500
135 I F A$="C or A$="c" THEN 4200
140 IF A$="D OR A$="d" THEN 5000
150 IF A$="S OR A$="s" THEN 6000
160 IF A$="E OR A$="e" THEN 7200
165 IF A$="J OR A$="j" THEN 7000
170 IF A$="Q OR A$="q" THEN END
180 GOSUB 3100:GOTO 80

Fig. 1-4. The System Diagnostic Main Menu Module listing.

serves to establish the keyboard map within the program. This map corresponds
to the column/row layout of the keyboard so that the appropriate keycap value
is displayed when a CTRL or COMMODORE (C~) key combination is pressed. This
is necessary because a character might display that is not indicated on the actual
keycap.

20 DATA "INST/DEL","RETURN","CRSR RT","F7","F1 ","F3","F6","CRSR

UP","3",IIW","A"
10 Getting Started

21 DATA "4","Z","S","E"," ","5","r","D","6","C","F","T","X","7",

"Y","G","8","8"
22 DATA "H","U","V","9","I","J","0"," M","K","O","N","+","P","L",
"-",".",":","@"
23 DATA "," ," + ","* ","," ,"CLR/HOME"," " I " /" 1 " 1" , "
"2","SPACE"
24 DATA" ","Q"

For example, at position 0 of this keyboard map is the INSERT/DELETE key, position
1 is the RETURN key, and position 2 is the CURSOR RIGHT key.

e128 USERS: In the C128 code, line 24 is expanded to include the 8, 5,

RUN/STOP, HELP, and TAB keys. There are also three additional lines of DATA
instructions to accommodate the function keys available exclusively on the
Commodore 128 keyboard. These include the LINE FEED, NO SCROLL, and
ARROW keys.

The FOR-NEXT loop at line 25 causes the 62 values assigned in the keyboard
map to be read into variable array R:

25 FOR I =0 TO 62: READ K$(I):NEXT

The (I) is the FOR-NEXT loop index, and this value determines that the characters
fall into keyboard map K$, a variable that is used later in the Keyboard Diagnostic
Module.

e128 USERS: The C128 code includes the 88 values assigned in the key-
board map to be read into variable array R.

Lines 30 and 35 initialize another array, designated as R, which is used later

for the Sprite Test in the Monitor Diagnostic Module:

30 DIM R(8):DATA 1,2,4,8,16,32,64,128

35 FOR I =0 TO 7:READ R(I):NEXT

e128 USERS: The C128 code has two additional lines at this point. The
first one loads an array with the CHR$ values of the eight function keys.
Line 37 is a FOR-TO loop which reads these values into the array. Refer
to Chapter 2, "How the Keyboard Module Works," for more information
on how this array is used. Refer to Appendix B for the actual C128 code
listing.

Lines 50 through 90 display the System Diagnostic Main Menu on the screen.
Line 50 calls up the Clear Screen subroutine at Line 2990, which clears the screen
and places the cursor at the top left corner. Then a series of PRINT commands
display the title and the various menu options:
 Commodore Care Manual 11

50 GOSUB 2990: PRINT TAB(12) "System Oiagnostic":PRINT:

60 PRINT TAB(3) "<K>eyboard Test <S>erial Comm Test"
70 PRINTTAB(3) "<M>onitorTest <O>iskOriveTest":
80 PRINT TAB(3) "<C>assette Test <J>oystick Test":
85 PRINT TA8(3) "<P>rinter Test <E>xerciser":
90 PRINT TAB(16) "<O>uit":PRINT:PRINT TA8(12) "Enter Selection"

Line 100 sends the program to line 3000 for the Get-a-Key subroutine:

100 GOSUB 3000 REM Get Key Command

When the user presses the key indicating the desired system module diagnostic
test, the CHR$ code value of the key is placed into variable A$.
Lines 110 through 170 check to see which key was pressed for a particular
menu choice. Each menu choice represents the diagnostic test for a different system
module, and is chosen by pressing the indicated character. Pressing K or k initiates
the Keyboard Diagnostic, just as pressing 0 or d initiates the Disk Drive Diagnostic,
and so forth.
When you press the designated key to choose a particular module test, the
program branches to the Get-a-Key subroutine, and the CHR$ code value of the
key pressed is placed into variable A$. If A$ is equal to K or k, then line 110
causes the program to branch to line 200, which is the beginning of the Keyboard
Diagnostic Module:

110 IF A$="K" OR A$="k" THEN 200

Likewise, if A$ is equal to M or m, then line 100 causes the program to branch

to line 800, the beginning of the Monitor Diagnostic Module:

120 IF A$="M" OR A$="m" THEN 800

This is also the case for lines 130 through 165:

130 IF A$="P" OR A$="p" THEN 3500

135 IF A$= "C" or A$= "c" THEN 4200
140 IF A$= "0" OR A$= "d" THEN 5000
150 IF A$="S" OR A$="s" THEN 6000
160 IF A$= "E" OR A$= "e" THEN 7200
165 IF A$="J" OR A$="j" THEN 7000

Line 170 is similar, but slightly different. This line checks to see if you have pressed
o or q, indicating that you are finished with the program and wish to "quit" out
of it:

170 IF A$= "0" OR A$= "q" THEN END

12 Getting Started

In this case, rather than branching to another module, the program simply ends,
and the system exits to the BASIC environment.
If the user does not press any of the valid keystrokes as presented in the menu,
the program falls through to line 180. Line 180 goes to the Beep subroutine at
line 3100:

180 GOSUB 3100:GOTO 80

After the beep, the GOTO statement branches the program back to Line 80 to
await another user keystroke.

THE UTILITY SUBROUTINES

The System Diagnostic Program employs five subroutines (Fig. 1-5) used
repeatedly throughout the code to execute program utility functions such as
clearing the screen or emitting a beep. These subroutines are the following:

D the Clear Screen subroutine

D the Get-a-Key subroutine
o the Beep subroutine
D the Key-to-End-Test subroutine
o the Key-to-Continue subroutine

The Clear Screen Subroutine

The Clear Screen subroutine consists of just one line. The commands within
line 2900 clear the screen and place the cursor at the top left corner of the screen:

2900 PRINT "{HOME/CLEAR)":RETURN:REM "Clear Screen Routine"

3000 GET A$:IF A$="" THEN 3000:REM "Get a Key Routine"
3005 K=PEEK(197):S=PEEK(653)
3010 RETURN
3099 REM "Beep Routine"
3100 FOR L=54272 TO 54296:POKE L,O:NEXT
3110 POKE 54296,15:POKE 54277,90:POKE 54278,1:
POKE 54273,21:POKE 54272,31
3120 POKE 54276,33
3130 FOR T=1 TO 50:NEXT
3140 POKE 54276,16:RETURN
3200 PRINT TAB(7)"press any key to end test";
3210 GOSUB 3000
3220 RETURN
3300 PRINT TAB(7)"press any key to continue":RETURN

Fig 1·5. The System Utility Subroutines.

 Commodore Care Manual 13

2900 PRINT" {HOME/CLEAR}" :RETURN:REM "Clear Screen Routine"

This is used to clear any messages or displays left on the screen before putting
up a new display. It also places the cursor in an appropriate location so that the
new display fits neatly within the limits of the screen. This subroutine is first
encountered at line 50, when the screen must be cleared and the cursor placed
at the HOME position before printing the System Diagnostic Main Menu on the
screen.

The Get-a-Key Subroutine

The Get-a-Key subroutine begins at line 3000 and is used throughout the
System Diagnostic Program. It is first encountered at line 100 in the Main Menu
Module. The system branches to this subroutine to actually get the key that has
been pressed on the keyboard. The value of this key is placed at the appropriate
place in the program to perform the function required at that time.

3000 GET A$:IFA$="" THEN 3000:REM "Get a Key Routine"

3005 K = PEEK(197):S = PEEK(653)
3010 RETURN

The GET command in line 3000 retrieves the user's keystroke directly from the
keyboard and places it into A$. The IF statement checks whether or not a key
has actually been entered. If no key is entered, then variable A$ is equal to a
null, meaning that there is nothing in the variable. The null is specified by the
two double-quotes:

3000 GET A$:IF A$="" THEN 3000:REM "Get a Key Routine"

As long as A$ is equal to null, the instruction loops back on itself continuously.

The loop is only broken when a key is pressed.
When a key is pressed, the program falls through to line 3005, which contains
two "PEEK" statements. A PEEK reads a value out of memory:

3005 K=PEEK(197)S=PEEK(653)

When the Get-a-Key subroutine gets a key for the keyboard test, the value of the
key is placed into memory location 197. Here, the program reads this value from
memory to use it as an index into the columnlrow matrix of the keyboard map,
which was built with the DATA statements starting at line 35. This index is used
later in line 595, where the program gets the key value from the keyboard map.
The second PEEK statement on line 3005 sets variable S to memory location
653. This memory location contains the SHIFT/C-/CTRL condition of the key that
has been pressed. If there is a zero in memory location 653, the SHIFT key has
not been pressed. If location 653 contains a one, the SHIFT key has been pressed.
If it contains a two, the c- key has been pressed. And if it contains a four, the
14 Getting Started

CTRL key has been pressed. (For further information about how these commands
function in the program, refer to "How the Keyboard Diagnostic Module Works"
in Chapter 2.)
The RETURN instruction sends the program back to where it was in the code
before it branched to this subroutine to get a key:

3010 RETURN

The Beep Subroutine

Because the Commodore 64 does not have a specific command or ASCII
character to create a beep, the Beep subroutine performs this function, using these
statements:

3099 REM "Beep Routine"

3100 FOR L=54272 TO 54296:POKE L.O:NEXT
3110 POKE 54296.15:POKE 54277.90 POKE 54278.1
POKE 54273.21 :POKE 54272.31
3120 POKE 54276.33
3130 FOR T =1 TO 50:NEXT
3140 POKE 54276,16:RETURN

The Commodore's built-in sound routines are used in this subroutine to produce
a beep to indicate an input error. This first appears in the Main Menu Module
at line 180, when the Beep subroutine is called up if the user presses a key that
is not a valid command key.
The Beep subroutine begins at line 3099 with a REMARK statement:

3099 REM Beep Routine

To produce sounds, Commodore uses machine language commands

expressed in numbers. A BASIC POKE statement lets you write values directly into
the memory locations where these numeric machine language commands reside.
Line 3110 begins with a FOR-NEXT loop including such a POKE statement:

3100 FOR L=54272 TO 54296:POKE L,O:NEXT

This line clears the Sound interface Device (SID) registers to prepare for subsequent
sound generation. A register is a special memory location that is an integral part
of the chip's circuitry. To clear the registers, a value of zero is "POKEd" into the
registers located at memory addresses 54272 through 54296.

(128 USERS: Line 3100 takes care of the entire Beep subroutine in the C 128
code, reflecting the use of the C128 beep character, CHR$(7). The POKE
and PEEK statements described below apply only to the C64 version of the
subroutine.
 Commodore Care Manual 15

Line 3110 consists of five POKE statements:

3110 POKE 54296.15:POKE 54277.90 POKE 54278.1:

POKE 54273.21 :POKE 54272.31

POKE 54296.15 sets the volume (at location 54296) at its highest setting
(represented by the value 15). If you wanted to make the volume of the beep
lower, you could enter a number smaller than 15.
POKE 54277.90 defines how fast the sound rises and falls from its peak level.
POKE 54278.1 defines the level to prolong a note. A value of one does not
hold the sound very long, because a quick beeping effect is desired in this instance.
POKE 54273.21 and POKE 54272.31 specify which note on the musical scale
the beep should be. If you were to refer to the Appendix of the Commodore User's
Guide, you would find a table of musical notes, with the high and low oscillator
frequencies. In this particular case, the note is an E.
Line 3120 is another POKE statement which sets a waveform. The value of
33 defines the resonance of the sound-how shrill or muted the tone is:

3120 POKE 54276.33

Line 3130 is a FOR-N EXT loop which is nothing more than a short delay loop.
This stops the execution of the Beep subroutine, because other than this loop,
there is actually no processing taking place in this line:

3130 FOR T = 1 TO 50:NEXT

This sets the duration that the note is to be played as the beep. For example, if
the TO value were set to 250 instead of 50, you would hear a quarter-note, which
is one standard musical beat. The value of 50 provides a very short, crisp beep
that seems to be the most appropriate for an alarm.
Li ne 3140 halts the beep:

3140 POKE 54276.16:RETURN

It then returns the program back to where it was in the code before it branched
to this subroutine to sound a beep.

The Key-to-End-Test Subroutine

The Key-to-End-Test subroutine consists of three lines:

3200 PRI NT TAB(7)" press any key to end test";

3210 GOSUB 3000
3220 RETURN

When the program branches here on a GOSU B instruction, the message - press
16 Getting Started

any key to end test" is displayed on the screen. Line 3210 sends this subroutine
to the Get-a-Key subroutine at line 3000. When a key is received in line 3000,
the program returns to the place in the program from which it came.

The Key-to-Contlnue Subroutine

The Key-to-Continue subroutine is a one-line instruction at line 3300:

3300 PRINT TAB(7)"press any key to continue":RETURN

This subroutine is used several times throughout the System Diagnostic Program
to allow the user to continue with the test at hand.

Program Modification and Adaptation

As you have seen, the System Diagnostic Program is written in Commodore
64/128 BASIC, and is structured to accommodate modification and additions.
You are not restricted, therefore, to simply testing the standard components
of a typical Commodore system. Should you purchase a new peripheral device
for your Commodore, such as a joystick, a different type of monitor, or a digitizer
pad, you can write a new diagnostic module for that device and add it to this
program. Chapter 9 covers the techniques, information, and references used for
writing diagnostics for new devices.

TOOLS AND RESOURCES

Troubleshooting and repairing computers, or for that matter any electronic
system, might seem to be a difficult task. However, most computer technicians
go about their work systematically, trying out various aspects of the system to
gather information about what the problem might be. They use this information
to make logical deductions as to the nature of the malfunction. They repair the
problem by making physical adjustments and replacing faulty components.
To perform such troubleshooting and repair, computer technicians have
specific knowledge and training about the particular systems they service. They
have complete sets of pertinent documentation and schematics. Technicians use
a good set of tools, and they have spare parts available to them. In addition, they
have various information resources from which to draw.
Although you cannot expect to do as thorough a job as a computer technician
without the same investment in training, tools, and spares, you can take cues by
learning some of their basic principles and techniques. Then when your computer
malfunctions, you'll be able to analyze the problem and get it repaired with a
minimum of effort and expense.

Documentation
Save all manuals, user guides, specifications, installation instructions, and any
other technical documentation that comes with your system, peripherals, and
upgrades. This documentation will provide the necessary specifics about your
particular Commodore configuration. This information is vital when installing and
setting up a new device, or if your computer malfunctions.
 Commodore Care Manual 17

If you have inadvertently lost or thrown out important documentation, you

can probably obtain a copy from your Commodore dealer, or send for one directly
from the manufacturer. You can also check with your library and your user's group
for documentation to borrow or buy.

Tools
Tools let you open, bend, cut, insert, and connect things in your computer.
The following tables list required tools, optional tools, and cleaning supplies. The
tools make the job of computer troubleshooting and repair possible. The clean-
ing supplies are vital, because cleaning is a major aspect of maintenance.
When you buy your tools, try to obtain good-quality tools. This does not
necessarily mean you should buy the most expensive ones on the market, but
you do want tools that will not bend or break at a critical moment. In other words,
buy dependable tools that will last a long time.
Table 1-1 lists required tools, and Fig. 1-6 illustrates these tools. Table 1-2
lists optional tools, and Fig. 1-7 provides their illustration. Table 1-3 lists clean-
ing supplies, and Fig. 1-8 illustrates them. The tables all list the functions, uses
and approximate costs for the tools and cleaning supplies.

Spares
Professional technicians usually have an inventory of spare parts for the
equipment they work on. The spares help them in troubleshooting, when they
swap out parts to find out whether or not it was that component that was causing
the problem. If the replacement solves the problem, then they know that the old
part was defective.
In your case, however, maintaining an inventory of spare parts for your
Commodore would be costly and impractical. An alternative to this is to find some-
one (a friend, a colleague at work, an acquaintance in a user's group) who also
owns a Commodore system. Work out a deal with this person enabling you to
temporarily swap parts with each other when one of your systems malfunctions.
You can use the other person's system for troubleshooting by temporarily swapping
suspect parts to find exactly where the problem is.

NOTE: Swapping parts from someone else's system should be used as a

last resort. Make sure both parties understand that there is a risk associated
with swapping. There is always the possibility that the particular problem
in your system could damage or destroy the swapped part. A good practice
might be to restrict swapping parts to major components, such as disk drives
and monitors.

Find out where you can get the best prices for computer parts. There might
be a good discount computer or electronics supply store in your area that stocks
computer components at lower rates than a computer retailer. The want ads in
18 Getting Started

wire strippers/cutters
'Is" flat-blade
needle -nose screwdriver
pliers %" flat-blade
screwdriver

Fig. 1-6. Required tools.

Table 1-1 . Required Tools, Use and Cost.

Average
Cost
to tighten and untighten
1/4" slotted screws for $3_50
1/4" flat-blade screwdriver
opening the system unit and
keyboard covers
to tighten and untighten
1/8" flat-blade screwdriver 1/8" slotted screws on $2_00
interface cables
to tighten and untighten
small Phillips screwdriver small cross-slotted screws $3_00
used for holding bolts down
to grip and/or bend
needle nose pliers small objects as an
$5-12.00
extension or a "helping
hand"
to grip and/or bend
pliers small objects, to hold larger $5.00
nuts
to cut wire, to strip away
wire strippers/cutters $5-12.00
plastic insulation
to tighten and unti!ilhten
screws in an electrically
non -conductive screwdriver charged environment such $2.00
as the monitor and power
supply
 Commodore Care Manual 19

socket
t
III r,\
~Id! small
wrench metal desoldering digital
set flat tool voltmeter &
file probes

Fig, 1-7, Optional tools,

Table 1-2. Optional Tools, Use and Cost.

.•..., . .'.. .i I .' ' . •. i t L'_ . "",' ., •.,., }
"' ,':-
"
,

'. '· ;r·<~:.' ,... ,i ,. . ". "-, ....',',.

to fit over hex head screws

socket wrench set of various sizes to tighten $15-25.00
or untighten
to smooth or grind down
small metal flat file a plastic surface such as a $3.50
keycap
to measure volts, ohms,
and amps in a power
digital voltmeter or multimeter
supply or interface board
$50-200
circuit
to melt and apply solder
in order to join or patch
fine-tip pencil-type soldering iron metal surfaces such as $20-25
cable wires, Ie leads,
components
the metal alloy used in
fine robin core solder soldering for joining metal $4-5.00
surfaces
to remove solder from
desoldering tool metal surfaces to $5~15.00
disengage them
solder tip sponge to clean up excess solder $1.50
20 Cetting Started

brush

Fig. 1-8. Cleaning supplies.

Table 1-3. Cleaning Supplies, Use and Cost.

)i ·.· ·.··· Y ~verag'

> , >i
Cleaning Supplies .• . i}i ...... i r;tM.
pressurized air used to
compressed air with nozzle and blowout dust and dirt
$5.00
extension from the keyboard and
printer
solution used to clean
6-oz can freon or contact cleaner contacts and switches on $5.00
PC board components
for general cleaning of
16-oz bottle isopropyl alcohol electronic hardware floppy
$1.00
disk drive heads, and print
wheels
for cleaning of hardware
cotton swabs and components in tight $2.00
places, such as disk drive
heads
for cleaning hardware
components, disk drive
sponges $1.00
heads, and print heads
with isopropyl alcohol
 Commodore Care Manual 21

the back pages of most computer magazines are good sources for used parts, as
are computer flea markets and swap meets.

User Resources
Computer resources become more and more important, the more involved
you become with your computer. It becomes less important to know everything
if you have good resources that provide you with accurate information.
If, after doing a bit of troubleshooting, you still can't find the problem, call
your local Commodore dealer. Most stores will assist you with valuable information
if you can ask specific questions.
Keep in mind that a friend of yours with a Commodore system might know
things you don't. Exchange information with any other Commodore users of your
acquaintance. Everyone's computer experience and knowledge is different.
Commodore user's groups are excellent repositories of information and
experience. You can find a local user's group through your computer dealer, in
your newspaper's computer page or social events page, or from listings in computer
magazines. The people you'll meet at a user's group can help you answer
questions, solve problems, and find other resources.
Read the Commodore computer magazines. They often provide good advice,
information, and further resources.

TROUBLESHOOTING AND REPAIR GUIDELINES

This book is broken down in chapters according to major computer
subsystems. If you're having trouble with your keyboard, turn to Chapter 2, "The
System Unit/Keyboard." The chapter explains possible keyboard problems, and
how to troubleshoot and repair them. Part of this troubleshooting process includes
running one of the diagnostic tests. The chapter goes on to tell you how to run
the diagnostic module and what results to expect. With the diagnostic modules,
troubleshooting is easy and automatic.
Once you run the diagnostic test and discover what the problem is, the general
repair guidelines offer suggestions on how to have the problem fixed. Many of
these suggestions have you doing the repairs. Even if you are not mechanically
or technically "inclined," you should have little problem troubleshooting your
Commodore, and perhaps even repairing some of the diagnosed problems.
If you run one of the diagnostic tests and the results indicate a problem, it
is a good practice to test the diagnostic on an identical system, particularly if you
have modified the program in any way. You want to ensure that the diagnostic
program is providing accurate results before spending any time and money on
repair.

LIMITS TO TINKERING
Never try to fix something for which you do not have the proper knowledge,
documentation, tools, or parts. A little knowledge can be dangerous, especially
when you know just enough to get yourself in trouble. You could make the prob-
lem worse.
22 Getting Started

Never attempt any procedure you feel you cannot handle. Do the easy repairs
first, and work your way up to the more difficult repairs as your skill and confidence
grow. When in doubt, let the professionals do it. Don't put your computer in
needless jeopardy.
Also, remember that a good technician does not tinker needlessly:

If it's not broken, don't fix it!

MAINTENANCE TECHNIOUES
A good computer technician performs general care and preventive main-
tenance on computers to minimize "downtime." Preventive maintenance and
good working habits are the two keys to system and component longevity. Many
system problems can be avoided if a few good habits are established.

General System Care

Everyday working habits are instrumental to the health of your computer.
Using dust covers, an anti-static mat, and a surge protector can go a long way
in preventing system problems.

Dust Covers. Buy dust covers to protect the monitor, system unit/keyboard,
disk drive, and printer. Dirt and moisture are your system's worst enemies. Dust
settles and collects on the contacts-the exposed wi res, or the legs, of the integrated
circuit (IC) chips on the system's printed circuit boards. These contacts have electric
current flowing through them, so that they become ionized, and attract particles
of dust. The dust attracts moisture out of the air. As this process continues, the
dust and moisture eventually cause electrical shorts and corrosion of the electronic
parts, which can then cause system malfunctions.
Spending $10 or $20 for a dust cover is preferable to buying a brand-new
printed circuit board to replace one that has been ruined by corrosion. Get into
the habit of coveri ng your system when not in use.

Static Electricity. Static electricity is another computer foe. The Ie chips

throughout your system contain minute electronic circuits that can be easily dam-
aged. These chips are particularly vulnerable to static electricity. If you live in
a dry, cool climate, your computer stands an even greater risk of getting "zapped."
Most devices within the computer are protected from electricity up to 2-5
kilovolts. However, the electrostatic discharge from a human can be more than
20 kilovolts. This means that you could actually be the source of static electricity
that can damage your system's components.
There are several ways to protect your computer from static electricity. You
can spray the floor or carpet around the system with an anti-static solution, or
you can lay down an anti-static mat under the computer. You can get anti-static
spray as well as an anti-static mat at an office or computer supply store. The least
expensive solution is to simply touch something metal that's not part of your
system, perhaps your desk lamp or file cabinet, before you touch the computer.
 Commodore Care Manual 23

This grounds you and keeps you from transferring static electricity to your
computer.
If you ever handle a printed circuit board, do not touch the metal edge
connectors. This will discharge the electricity in your body through the printed
circuit board to the nearest IC chip.

Power Surge Protection. The electricity at the wall sockets is rated at 110/120
volts at 60 Hertz (cycles per second). There are moments when surges of electricity
exceed 110/120 volts, and other moments when sags in voltage are lower than
normal. You've probably experienced drops in electricity when your lights dim.
This "brown-out" effect might cause your keyboard to temporarily lock up, and
you might lose some data due to logic-related problems within the computer.
The most damaging problem is the voltage surge. A power surge can pass
through your power supply's filter circuits by giving it more peak voltage than
it can effectively suppress. Your computer's power supply takes the 110/120 volts
ac and rectifies it to 5, 12, or 15 volts de. These are the voltages with which the
integrated circuits in the computer are designed to operate. When the computer's
power supply receives a large power surge, it is not capable of suppressing it.
This instantaneous spike is sent through to the chips, damaging or even destroying
them.
Because boards and many chips are expensive to repair and replace, protect
the computer from these indiscriminate surges by using a surge protector.
A surge protector isolates the voltage spikes in order to provide the system
with a constant 11 0/120-volt supply. Obtain a surge protector at a computer or
electronics supply store. Using a surge protector with your computer extends the
life of its integrated circuits.

Food and Drink. Don't eat or drink near your computer. If you spill or drip
something into your keyboard, you'll have an emergency cleaning job on your
hands, or even the instant need for a new keyboard. Because the keyboard and
system unit are included in the same housing, any liquid that spills in the keyboard
could seep into the system unit, causing far more serious problems, such as shorting
components out and causing permanent damage.
Cookie crumbs, sandwich particles, and dinner bits can all end up inside your
keyboard and system unit, if you eat while working. This can destroy the keyboard
contacts and render your keyboard useless. It can also damage components of
the system unit.

Preventive Maintenance
You should perform the following preventive maintenance procedures for
your computer at least every three months. These procedures keep your system
clean and in adjustment, thereby warding off possible problems.

Vacuum/Compressed Air. Use a hand-held vacuum cleaner or can of

compressed air (like camera lens cleaner), to vacuum or blow around components
such as the keyboard keys (Fig. 1-9), or the printer mechanism. This clears out
any dust and dirt that gets into the workings in spite of the dust cover.
24 Getting Started

Fig. 1-9. Dusting the keyboard with compressed air.

If you have a choice between the two, it's preferable to vacuum dust up rath-
er than blow it around. Blowing dust can possibly send it deeper into the system,
where it might cause even more trouble _

Cleaning. Certain parts of your system can become dirty through continuous
use. The floppy disk drive head, the daisy print wheel, or the dot-matrix print
head can accumulate a layer of oxidation or dried ink.
Disk drive head cleaning kits are available at most computer stores for
approximately six dollars. Insert a special diskette permeated with a cleaning
solution, enter a command that causes the diskette to rotate, and the read/write
heads are cleaned in a flash.
If you use a cassette drive with your system, you can get cassette cleaner from
a record or stereo store. You can also use cotton swabs lightly moistened with
isopropyl alcohol to clean the read/write heads of the cassette drive.
A gauze cloth soaked in isopropyl alcohol (not rubbing alcohol) can be used
to clean daisy wheels and dot-matrix print heads. Isopropyl alcohol can also be
used to clean the exterior or interior of your system where dirt and dust have
accumulated. Use cotton swabs lightly moistened with isopropyl alcohol to clean
hard-to-reach areas .

Loose Cables. Several cables may be connected to the system unit at the rear
and side. These cables connect interface circuits to the peripheral devices. The
cable connectors are plugged into the system unit's receptacles . If the cable
includes screws, they should be tightened down. These cables loosen when, for
example, you move the printer or bump the modem. Suddenly a peripheral stops
working because it's not getting the proper connection .
The solution to this is to use a small screwdriver and secure the cable into
 Commodore Care Manual 25

its receptacle. If the cable does not have screw mounts, then simply make sure
it is correctly pressed into the receptacle.

Troubleshooting Techniques
"Troubleshooting" is another word for problem-solving. You have a computer
malfunction, and you want to systematically go about discovering what caused
it so you can effect a repair.
Start with the easy things first:

D Does it have power? Is the fuse burned out?

D Are all the connectors properly seated?
D Are all power switches turned to the ON position?

Each subsystem chapter that follows lists several more specific solutions to try
when troubleshooting a problem.
When you've tried everything and the problem still is not fixed, the system
unit itself is often involved. Refer to Chapter 2, "System Unit/Keyboard" for system
unit troubleshooting procedures.
If those system unit measures do not effect a repair, it's time to take the
computer in for servicing.

WHAT TO DO FIRST
To get started on the general care, preventive maintenance, troubleshooting,
and repair of your Commodore, do the following:

D Read through this book to familiarize yourself with the concepts and
organization of the material. This way you can get started immediately with
preventive maintenance, and when a problem arises, you'll know right where
to look.
D Make a backup of the System Diagnostic Program. If you did not purchase
the program diskette, key in all the diagnostic programs now, before any prob-
lems arise. Then if something does go wrong, you'll already be prepared to
troubleshoot.
D Gather at least the basic tools and cleaning supplies into a computer
maintenance kit.
n Collect all the technical documentation you have and find a central place for
it, such as an area at your desk or bookcase, or in a binder.
U Contact someone who also owns a Commodore system, and agree to loan
and borrow components when needed for troubleshooting. Start establishing
your computer user resources.
n Tryout the diagnostics now, before you have a problem. Know how the results
are supposed to appear under normal circumstances.
D Code any necessary modifications into the System Diagnostic Program. These
modifications might have to do with accommodating another peripheral, or
26 Getting Started

a different kind of system, printer, or keyboard than what is allowed in this

program. Test the modified program thoroughly, and when you're satisfied
that the program is working as it should be, make a backup copy.

If you follow these measures, you'll be ready to troubleshoot and repair at

the first sign of a suspected computer malfunction.
 Chapter 2
The IYllte. Uaitl
Keylb ••rd
The system unit is the "brains," of the computer-the controller and coordinator
for everything that takes place. It directs the activities of peripheral devices, issues
commands, and processes input and output. Commands and data are input to
the system unit for processing via the keyboard, which is the primary external
link to the computer. The Commodore houses the system unit and keyboard within
the same unit.

DESCRIPTION AND FUNCTION OF THE SYSTEM UNIT

The system unit consists of the following:

o central processing unit (CPU) and associated support chips

o random-access memory
o serial bus
o receptacles for optional peripheral devices such as the printer and modem
o operating system or basic input/output system (BIOS), which operates using
read-only memory devices (ROMs).

Although there is no specific system unit module within the System Diagnostic
Program, the modules testing each of the subsystems perform a sufficient job of
exercising the system as a whole. This is because all subsystems are connected
into and controlled by the system unit.

27
28 The System Unit/Keyboard

DESCRIPTION AND FUNCTION OF THE KEYBOARD

The keyboard is used to enter data, commands, and selections to work with
your application software, whether the data are numbers in a spreadsheet, words
in a word processor, or records in a database. The keyboard is your Commodore's
primary input device.
The Commodore uses an integral keyboard, meaning it is housed together
with the system unit. The CPU, memory, interfaces, and keyboard are all contained
in one housing (Fig. 2-1).
The key set found on all standard keyboards consists of the "QWERTY"
typewriter keys (named for the first six alphabetic characters found on a typewriter),
arrow cursor keys, and CONTROL, INSERT, and DELETE keys. The C64 keyboard is
a standard keyboard like this.
More "deluxe" system keyboards such as the C128 keyboard also include
a ten-key pad, additional arrow cursor keys, programmable function keys, and
other special function keys such as CAPS LOCK, NO SCROLL, and ALT (Fig. 2-2).

How the Keyboard FunctIons

Regardless of how basic or deluxe a keyboard is, however, they all work
according to the same principle: pressing a key sends a code to the CPU in the
system unit for translation and processing.
This is similar to throwing a light switch or pressing a button on your television
to change channels. The key makes contact and causes a unique "code" to be
placed into a keyboard buffer. What this code consists of depends upon which
key or key combination has been pressed.
The matrix of key and key-combination code is referred to as a hard-wire
mapping of the keys. When you press a key, an electromechanical process takes
place to generate a column and row value, indicating the keyboard location from
where the key came.

Fig. 2·1 . Commodore 64 keyboard.

 Commodore Care Manual 29

Fig. 2-2. Commodore 128 keyboard.

The physical action of pressing the key causes the CPU, which interfaces with
the keyboard, to gather the column and row information, indicating where the
key is located on the keyboard. The CPU also discerns whether the SHIFT, CTRL,
or c- (Commodore logo) key is pressed.
This information is sent into a program residing within the kernel portion of
the system's read-only memory (ROM), and it is here that the calculations are
made about what the keystroke actually is and what it is expected to do.
The kernel handles input (keyboard) and output (monitor), or I/O functions
for the Commodore. In this case, it takes the character and transfers it to the
keyboard buffer_ Further processing in turn transfers the character to the monitor's
screen memory, thus displaying the character on the screen_

TROUBLESHOOTING AND REPAIR GUIDELINES

This section describes the problems that the system unit and keyboard could
experience_ It explains what causes these problems, and details the steps to fix
them.
In subsequent chapters covering troubleshooting procedures for each of the
subsystems, you'll learn that if nothing happens at all to begin with, the system
unit is the suspect component to troubleshoot. In addition, if you try all the
troubleshooting suggestions for a particular subsystem, but still cannot find the
problem, again, the problem is likely to be within the system unit. Those sections
direct you to this section to find and repair the system unit problem_

Problem: The Keyboard Doesn't Work At All

If you press keys on the keyboard, and nothing happens on the screen, this
means the keyboard is not making contact. The character signals are not bei ng
sent through the system unit to be displayed on the screen_
30 The System Unit/Keyboard

B Solutions

[] The first thing to check is whether or not the system unit's red LED power
light is illuminated. If it is not lit, the system unit is not getting power. Check
your electrical outlet, the power strip if applicable, the wall switch if applicable,
and the fuse box or circuit breaker.
If these are all in order, the next thing to do is check the system's power sup-
ply. This is a fairly simple procedure, because the power supply is external
to the system (Fig. 2-3). Remove the power supply and swap it on another
Commodore system. If that system does not power up either, then buying and
installing a new power supply will solve your problem. A Commodore power
supply costs approximately $40.
o If the red LED light is illuminated, but the keyboard does not work, check
the monitor for your standard screen prompts. These prompts indicate that
you are in the BASIC environment by displaying the word READY and then
a block cursor. If you do not see any of these, there is likely to be a problem
with the system unit. Turn the computer off, Make sure the power supply cable
is securely connected to the system, and turn the computer on again. If the
screen display still does not look right, take the system unit in for servicing.

o If the red LED is illuminated and the system prompts are displayed correctly
on the screen, but the keyboard still does not work, this indicates a keyboard
problem rather than a system unit problem. Follow these steps:
1. Turn the system off.
2. Disconnect the power supply.
3. Disconnect all attached peripheral devices (cassette drive, disk drive,
printer, monitor, etc.).
4. Remove the screws from the bottom of the system unit (Fig . 2-4).
5. Open the system unit. You'll see a ribbon cable running from the keyboard
onto the printed circuit board containing the CPU chip and many other

Fig. 2-3. System unit and power supply.

 Commodore Care Manual 31

Fig . 2-4. Removing the system unit screws.

integrated circuits (Fig . 2-5). This board is referred to as the motherboard

or system board.
6 . Disconnect the ribbon cable from the board side and check the pins for
oxidation. Over a period of time, oxidation can form on the cable pins
and edge connector. Oxidation is caused by contact with air, moisture,

Fig. 2-5. Opening the system unit.

32 The System Unit/Keyboard

or a combination of the two in humidity. Oxidation tarnishes the metal,

and can look like either a dull gray or black film.
7. If there is oxidation, remove it with a pencil eraser (Fig. 2-6) . You can
also use an emery cloth, very fine sandpaper (400-800 grit), or a lint-free
cloth moistened with isopropyl alcohol.
8. Connect the cable to the edge connector again, close the system unit,
reconnect the power supply and monitor, turn on the system unit, and
check to see if the keyboard works now.
o Another possibility is that the integrated circuit chip which controls the
keyboard circuitry has a problem. Take the system in for servicing, tell the
technician that you did see the monitor prompts and have checked the
keyboard connections. The technician can then check the keyboard IC, and
if that's the problem, it can simply be replaced.

o If the keyboard circuitry is not the problem, replace the keyboard. Replacement
keyboards are available through a Commodore dealer, service center, or
magazine mail order. However, the keyboard should not need to be replaced
unless it has been handled roughly or dropped.

Problem: Particular Keys Do Not Work

You might be typi ng along and notice what looks I ike a "typo." Perhaps there
is an "a" that was left out of a word. You go back to the word and type the "a"

Fig. 2·6. Erasing oxidation.

 Commodore Care Manual 33

Fig. 2-7. Removing a key.

where it's supposed to be, but nothing happens; the "a" simply is not working,
while all the other keys are working fine.
First run the Keyboard Diagnostic Module and confirm that the key does not
work.
l2i Solution

o If the key does not work, use a flatblade screwdriver, or better yet, a key
removal tool, to lift the key from the keyboard (Fig. 2-7). Spray contact cleaner
on the key post (Fig. 2-8). Contact cleaner is available at electronics stores.
Replace the keycap on the post and try it again. If the key still does not work,
the keyboard might have a more serious problem; take it in for servicing.

Problem: Keys Stick When Pressed

A sticking key stays down when you press it, causing its character to fill up
the whole screen until you pry the key up again. There are three remedies for
this problem.

Fig. 2-8. Spraying contact cleaner on the key post.

34 The System Unit/Keyboard

c;::: Solutions

[l Lift the key off and spray contact cleaner on the key post as described in the
previous solution. This clears off any dust or dirt that might be obstructing
the free movement of the key.

II Remove the keyboard cover from the bottom. Take a flat file and slightly file
the cutout in the case where the key is binding. This makes the receptacle
larger, so the key doesn't fit so tightly.

o If the key is not binding on the case, pop the key off and lightly file the edges
of the key itself (Fig. 2-9). This should loosen the fit between the key and the
key case so that the key can move more freely and no longer stick.

Problem: A Key Doesn't "Feel" Right

As a keyboard ages, some of the more frequently used keys will begin to feel
"mushy," or at least not as solid as the other keys. This is because the key springs
soften as they get older.

'2J Solutions

D Call around to computer retailers to find keyboard springs for your keyboard.
Lift off the keycap and then remove the spring from its post (Fig. 2-10). Re-
place the old spring with the new, and pop the keycap back on.

D If you can't find a replacement spring, use one from the keyboard that is rarely
used. It could be one of the function keys, or perhaps one of the numbers
on the 128 ten-key pad.

RUNNING THE KEYBOARD DIAGNOSTIC MODULE

The Keyboard Diagnostic Module consists of the Echo Key Test. This test
displays, or echoes, any key pressed on the keyboard. If you press a special

Fig 2-9. FII·ng the edges of the key.

 Commodore Care Manual 35

Fig. 2-10. Removing the key spring from the post.

character or key combination, the name of the character or combination is

displayed.
There are two graphic character sets available on the Commodore. The first
character set is the uppercase-only mode (set 1). The second character set is the
upper/lowercase mode (set 2). To switch between the two modes, press the SHIFT
and C = keys simultaneously (Fig. 2-11). Only one character set can be active at
a time.
The graphic characters available with each of these character sets are shown
on the front of the key caps. There are two characters: one on the left, and the
other on the right (Fig. 2-12). If you're in the upper/lowercase mode, and you
press the c= key with one of the keys, the graphic character shown on the left
side of the key is displayed on the screen. If you're in the uppercase mode and
you press the c= key with one of the keys, the graphic character on the right
side of the key is shown.
The System Diagnostic Program automatically shifts into the default
upper/lowercase mode when it's run. However, in the Keyboard Diagnostic, you
can choose either character set. An informational message is displayed, indicating
which character set is currently active. The menus and prompts also switch to
the current character mode. In other words, if the upper/lowercase mode is active,
all command prompts are displayed in upper/lowercase letters. If you press the
SHIFT and the c- key while in the Keyboard Diagnostic, the menu shifts to all
uppercase characters.
In either mode, when you press the c= key to test a graphic character, the
resulting graphic character and its graphic CHR$ code are displayed.
The CHR$ code values are used to represent the standard display characters
(such as A through Z), special control functions like CURSOR LEFT and CLEAR SCREEN,
special graphic characters and symbols, and reverse video characters as a numeric
code. The Commodore recognizes 256 such CHR$ code values. The CHR$ code
36 The System Unit/Keyboard

Fig. 2-11. Switching between the two character modes.

value is often used in BASIC programs to access a particular symbol or function

that is not directly accessible from the keyboard. For example, on the Commodore
64, the BASIC command PRINT CHR$(83) displays a heart symbol.
The Commodore CHR$ code values are similar, but not identical, to the ASCII
(American Standard Code for Information Interchange) code. Many personal
computers map their keyboard characters and other special functions to ASCII
values . The Commodore 's CHR$ code is a variation of ASCII.

Fig. 2-12 . Graphic characters.

 Commodore Care Manual 37

When running the Keyboard Diagnostic Module, press a key to test whether
it's working properly. This diagnostic should read and display, or echo, this key.
The echo test lets you check whether or not a particular key, or even the entire
keyboard, is working.
The Keyboard Diagnostic Module also displays the CHR$ value of the key.
This lets you check whether the keys are sending the proper code to the computer
to display the proper character or function. The Commodore User's Guide that
is provided with your system includes a table that shows which key and/or function
each CHR$ code value is meant to provide.
To run the Keyboard Diagnostic Module, follow the instructions provided
in "Running the Diagnostic Program" in Chapter 1. Then press K or k to initiate
the Keyboard Diagnostic Module.
Following the instructions given, press any key you wish to test. You can test
any key on the keyboard: alphanumeric keys, cursor keys, function keys, special
CTRL or c~ keys. The key you press is displayed along with its CHR$ code value
and any applicable key combination (Fig. 2-13).
If a character other than the one you pressed is displayed, or if no CHR$ code
value is displayed, then you have accomplished the first troubleshooting step:
there is something wrong with your keyboard. Refer to "Troubleshooting and Re-
pair Guidelines" earlier in this chapter to get the keyboard working properly again.
When you finish testing, press the CLR/HOME key, and the program should
return to the System Diagnostic Main Menu. If this does not happen, the CLR/HOME
key is failing. In that case, press the RUN/STOP key to end the program, then
troubleshoot the CLR/HOME key.

Keyboard Diagnostic Module

Character Value Key Combination Set

Fig. 2-13. The Keyboard Diagnostic Module.

38 The System Unit/Keyboard

HOW THE KEYBOARD MODULE WORKS

When the user presses K or k from the main menu, the System Diagnostic
Program branches to line 200, where the Keyboard Diagnostic Module begins.
Figure 2-14 is a complete listing of the Keyboard Diagnostic Module.
Line 200 is a REMARK statement indicating the beginning of the Keyboard
Diagnostic Module:

200 REM" Keyboard Diagnostic Module"

C128 USERS: The C128 code has an additional line, 205, which changes
the values of the function keys so that they will actually display their
keynames (Fl, F2, F3, etc.) during this test, rather than displaying the code
for their programmed functions. This replaces the function keys' current pro-
gramming; however, their default designations are stored in system ROM.
Turn the system off and on again to restore the function keys to their original
programming after you have run this test.

Actual processing begins at line 210. The first command is a POKE statement,
which places a value directly into a particular memory location. In this case, the
program places a value of 23 into memory location 53272. This sets the character
mode to set 2, the upper/lowercase mode.

210 POKE 53272,23:S1 = 1 GOSUB 630

The character set information indicating whether character set 1 or 2 is currently

active is placed into variable S1, This instruction reflects the action of the POKE
command, which caused the character set to be the upper/lowercase mode.
The next instruction is a COSUB to line 630, which displays the headings
on the monitor screen for the Keyboard Diagnostic Module.

C128 USERS: The 128 code uses a different POKE location and value in
line 210.

Line 220 indicates that until the user enters a key to be placed in variable A$,
variable KY$ remains null. Variable KY$ holds the display indications of any CTRL
and c ~ key combinations, such as GRL A, for later use in the test display.

220 A$ = "" KY$ = "" :GOSUB 3000

The COSUB instruction returns the program to the Get-a-Key subroutine at line
3000. As soon as the user presses a key to be tested, the Get-a-Key subroutine
breaks its continuous loop, and the program continues on to line 230.
Line 230 sets variable N equal to the CHR$ value of A$, which is the variable
holding the keystroke:

230 N = ASC(A$)
 Commodore Care Manual 39

200 REM"Keyboard Diagnostic Module"

210 POKE 53272,23:S1=1:GOSUB 630
220 A$="":KY$='''':GOSUB 3000
230 N=ASC(A$)
260 IF ASC(A$)=19 THEN GOTO 740
270 IF ASC(A$)=5 THEN KY$="ctrl 2:GOTO 600
280 IF ASC(A$)=17 THEN A$=" ":KY$="crsr down":GOTO 600
290 IF ASC(A$)=18 THEN KY$="rvs on":GOTO 600
300 IF ASC(A$)=20 THEN A$=" ":KY$="inst del":GOTO 600
310 IF ASC(A$)=28 THEN KY$="ctrl 3":GOTO 600
320 IF ASC(A$)=29 THEN A$=" ":KY$="cursor right":GOTO 600
330 IF ASC(A$)=30 THEN KY$="ctrl 6":GOTO 600
340 IF ASC(A$)=31 THEN KY$="ctrl 7":GOTO 600
350 IF ASC(A$)=141 THEN KY$="shift return":GOTO 600
360 IF ASC(A$)=142 THEN KY$="upper case":GOTO 600
370 IF ASC(A$)=144 THEN KY$="ctrl 1":GOTO 600
380 IF ASC(A$)=145 THEN KY$=" ":KY$="cursor up":GOTO 600
390 IF ASC(A$)=146 THEN KY$="rvs off":GOTO 600
400 IF ASC(A$)=147 THEN GOTO 740
410 IF ASC(A$)=148 THEN A$=" ":KY$="inst del":GOTO 600
420 IF ASC(A$)=156 THEN KY$="ctrl 5":GOTO 600
430 IF ASC(A$)=157 THEN A$=" ":KY$="cursor left":GOTO 600
440 IF ASC(A$)=158 THEN KY$="cntrl 8":GOTO 600
450 IF ASC(A$)=159 THEN KY$="ctrl 4":GOTO 600
460 IF ASC(A$)=133 THEN KY$="f1":GOTO 600
470 IF ASC(A$)=134 THEN KY$="f3":GOTO 600
480 IF ASC(A$)=135 THEN KY$="f5":GOTO 600
490 IF ASC(A$)=136 THEN KY$="f7":GOTO 600
500 IF ASC(A$)=137 THEN KY$="f2":GOTO 600
510 IF ASC(A$)=138 THEN KY$="f4": GOTO 600
520 IF ASC(A$)=139 THEN KY$="f6":GOTO 600
530 IF ASC(A$)=140 THEN KY$="f8":GOTO 600
560 IF S=O OR S=1 THEN 600
570 IF S=2 THEN KY$="C= ":GOTO 595
580 IF S<>4 THEN GOTO 710
590 KY$="CTRL "
595 KY$=KY$+K$(K)
600 GOSUB 630
610 PRINT TAB(5) A$;TAB(13) N;TAB(23) KY$;TAB(35) S1
620 GOTO 220
630 GOSUS 2990
640 V=PEEK(53272)
650 IF V=21 THEN S1=1:GOTO 680
660 S1=2:PRINT TAS(7) "Keyboard Diagnostic Module":PRINT
40 The System Unit/Keyboard

670 PRINT TAB(2) "Character VaLue Key Combination Set":GOTO 700

680 PRINT TAB a) "keyboard diagnostic rroduLe":PRINT
690 PRINT TAB(2) "character vaLue key combination set"
700 PRINT TAB(2)"--------- ----- --------------- ---":RETURN
710 GOSUB 630
720 PR INT "An ill ega 1 sh i f t code was encountered!"
730 PRINT "your keyboard needs service": GOTO 220
740 POKE 53272,23:PRINT "(BLUE}":GOTO 50

Fig. 2·14. The Keyboard Diagnostic Module listing.

This is done because some keystrokes cause some type of cursor movement.
Ordinarily, the program prints the value held in A$ to display the graphic character.
However, if it's a special character that causes a cursor movement, the program
changes A$ to a blank so that the test display is not disrupted. Still, the CHR$
value of the key must be indicated, even though there is no graphic indication
of the keystroke itself. So the program sets N to the CH R$ value of A$ before
processi ng.
After this, line 260 checks to see if the CHR$ value of A$ is equal to 19.
If it is, this indicates that the user has pressed the CLRiHOME key, which causes
the program to go to line 740 to begin an exit subroutine:

260 IF ASC(A$) = 19 THEN GOTO 740

The program performs some "housekeeping" routines before exiting back out
to the System Diagnostic Main Menu, and these routines are found at line 740.
If the value of A$ is not equal to 19, the prograrn falls through to line 270.
Lines 270 through 530 check for exception keys, such as cursor movement keys,
the RETURN key, color modes, and keys for which there is no actual graphic display
character:

270 IF ASC(A$)=5 THEN KY$="ctrI2:GOTO 600

280 IF ASC(A$) = 17 THEN A$=" "KY$="crsr down"GOTO 600
290 IF ASC(A$) = 18 THEN KY$="rvs on":GOTO 600
300 IF ASC(A$) =20 THEN A$=" "KY$="inst del"GOTO 600
310 IF ASC(A$) =28 THEN KY$="ctrI3"GOTO 600
320 IF ASC(A$) = 29 THEN A$ =" ":KY$ =" cursor right"GOTO 600
330 IF ASC(A$) =30 THEN KY$="ctrI6":GOTO 600
340 IF ASC(A$) =31 THEN KY$="ctrl 7":GOTO 600
350 IF ASC(A$)=141 THEN KY$="shift return" GOTO 600
360 IF ASC(A$) = 142 THEN KY$ = "upper case"GOTO 600
370 IF ASC(A$) = 144 TH EN KY$ =" ctrl 1 "GOTO 600
380 IF ASC(A$) = 145 THEN KY$=" ":KY$="cursor up":GOTO 600
390 IF ASC(A$) = 146 THEN KY$="rvs off"GOTO 600
400 IF ASC(A$) = 147 THEN GOTO 740
410 IF ASC(A$) = 148 THEN A$=" ··KY$="inst del"GOTO 600
420 IF ASC(A$) = 156 THEN KY$="ctrl 5"GOTO 600
 Commodore Care Manual 41

430 IF ASC(A$)=157 THEN A$=" ":KY$="cursor left":GOTO 600

440 IF ASqA$) = 158 THEN KY$="cntrI8":GOTO 600
450 IF ASqA$) = 159 TH EN KY$ = "ctrl 4" :GOTO 600
460 IF ASC(A$) = 133 THEN KY$="f1":GOTO 600
470 IF ASC(A$) = 134 THEN KY$="f3":GOTO 600
480 IF ASqA$)=135 THEN KY$="15":GOTO 600
490 IF ASC(A$) = 136 THEN KY$= "17"GOTO 600
500 IF ASqA$) = 137 THEN KY$="f2":GOTO 600
510 IF ASC(A$) = 138 THEN KY$="f4":GOTO 600
520 IF ASqA$) = 139 THEN KY$ = "16"GOTO 600
530 IF ASC(A$)=140 THEN KY$="f8":GOTO 600

This exception check is done for these particular keys so that these functions are
not actually displayed. To prevent any disruption to the screen displays effected
by these keys, variable A$ is set equal to null for each of these special cases.
The color commands are not "trapped" in this manner other than to display
their key combinations. If the user activates the color green while in this test,
for example, the display changes to green. This lets you test the key combinations
used to obtain the different colors. As part of the "housekeeping" routine start-
ing at line 740, the program resets the screen color back to the default of light
blue before returning to the Main Menu.
Taking line 270 as an example for these exception cases, you see the following:

270 IF ASqA$)=5 THEN KY$="ctrl 2":GOTO 600

The value 5 returned from a character variable (CHR$) means that the user pressed
CTRI 2, which sets one of the colors. The variable KY$ stores the key combination.
The program branches to line 600 for the actual test processing, because now
that the program has received a user keystroke, the keystroke can be processed.
As you can see, there are quite a number of these exception checks. This
ensures that all keys and all combinations can be tested. Some key combinations
produce a color, as in the example at line 270. Other key combinations produce
graphic characters. An example of this is pressing SHIFT 1 to have the! symbol
displayed and tested. Other examples include the graphic characters returned when
the C ~ key is pressed alone or in combi nation with the SHIFT key to get one of
the graphic characters displayed on the right or left of the keycap legend. This
test lets the user know which key combination was pressed to display the graphic
character.

e128 USERS: Three additional lines are added in the C128 code for this
section: lines 272, 273, and 315. These I ines provide exception checks for
the TAB, LINE FEED, and ESC keys, respectively, which are not available on
the C64.

If the user does not press any of these exception case keys, the program falls
through to line 560.
Line 560 is an IF statement which sends the program to line 600 if variable
42 The System Unit/Keyboard

5 contains a zero or a one, indicating a nO-SHIFT or SHIFT condition, respectively.

At this point, these character conditions are considered "normal"; they require
no special handling.

560 IF S=O OR S= 1 THEN 600

However, if variable 5 were equal to two or four, a special character combination

involving the c- or CTRL key would be indicated. In that case, the program would
fall through to line 570.
Line 570 is another IF statement, indicating that if variable 5 is a two, then
variable KY$ is set equal to c-, to represent the c- key in the display:

570 IF S=2 THEN KY$= "c- "GOTO 595

The program then branches down to line 595.

If S is not equal to two, the program falls through to line 580:

580 IF S< >4 THEN GOTO 710

If variable 5 is not equal to four, the program falls through to line 710, which
is an error routine signaling that an improper SHIFT condition, and possibly a
keyboard problem, exists.

C12B USERS: Line 580 is modified in the C128 code to handle the ALT key
available from the C128 keyboard, which offsets the possibility of such an
improper SHIFT condition.

If variable 5 is equal to four, the program falls through to line 590:

590 KY$ = "CTRL "

Line 590 sets variable KY$ to CTRL for the display of the key combination. The
program then falls through to line 595.
Line 595 goes to the keyboard map and retrieves the other character that was
pressed in combination with the c- or CTRL key. This key is held in variable K$(K),
the character value index that was retrieved from memory in line 550. The (K)
holds the position of the major keycap from K$:

595 KY$ = KY$ + K$(K)

At this point, the program finally has all the information necessary to actually
display the test results of the key(s) pressed, and can proceed to line 600.
Line 600 is a CaSUB to line 630. Line 630 starts the routine which prints
the Keyboard Diagnostic Module headings, such as "Character," "Value," and
so forth:

600 GOSUB 630

 Commodore Care Manual 43

After the headings are displayed, the program returns to line 610. This is the line
that actually prints the test results of the pressed key(s):

610 PRINT TAB(5) A$;TAB(13) N;TAB(23) KY$;TAB(35) 81

It tabs the display over five columns, then prints the contents of variable A$, which
is the actual graphic character. Of course, if the pressed key(s) were an exception
of some type, nothing would display in this field, because the exceptions were
set to blanks to prevent the display from being adversely affected by the function.
Then the display tabs to position 13, and the contents of variable N is printed.
At the start of this module, the CHR$ value of A$ was set to N. This was done
for the exception keys which were converted to blank letters. If the actual
CHR$(A$) were printed here, you would probably see just a blank, or a value
of 32, which would not be useful information. So N holds the actual CHR$ code
value of the key(s) that is being tested.
Next, the line tabs to position 23, and the key combination is printed, for
example, CTRL 4. Finally, the line tabs to position 35, and either Sl or S2 is
pri nted, to tell you which graphic character mode the system is currently
employing, set 1 or set 2.
Line 620 sends the program back to line 220, the location where the program
looks for another keystroke to test:

620 GOTO 220

This completes the process of analyzing the keystroke.

Line 630 begins the subroutine that displays the module's test title and
headings. The first order of business for this subroutine is to clear the screen and
place the cursor in the upper left corner HOME position.

630 G08UB 2990

This is done with the Clear Screen subroutine at line 2990.

Line 640 is another PEEK instruction to read a value stored in memory. In

this case, the program reads from memory location 53272, and places the value
into variable V:

640 V = PEEK(53272)

Location 53272 holds the data indicating which graph ic character set is currently
active-the uppercase-only mode (set 1), or the upper/lowercase mode (set 2).

(128 USERS: Line 640 in the C128 code is modified for a different PEEK
location of the current graphic character set.

Li ne 650 then has a related IF statement: if variable V contai ns 21, then the
44 The System Unit/Keyboard

variable S1, which holds the graphic character set information, is set 1, the
uppercase mode.

650 IF V = 21 THEN S1 = 1 :GOTO 680

If this statement is true, the program branches down to line 680.

(128 USERS: The (128 code is modified at line 650 to handle the different
value of V for the character set mode.

If the statement in line 650 is not true, the program falls through to line 660,
which assumes that if variable V is not a 21, then it must be a 23. The value 23
indicates that graphic character set 2 is active for the upper/lowercase mode.

660 S1 =2:PRINT TAB(7) "Keyboard Diagnostic Module":PRINT

Line 660 first sets variable S1 to two for the upper/lowercase mode. Then it prints
the title of the Keyboard Diagnostic Module followed by a blank line.
Line 670 goes on to print the test headings:

670 PRINT TAB(2) "Character Value Key Combination Set":

GOTO 700

Then the program falls down to line 700.

If character set 1 had been in effect, the program would have branched from
line 650 to line 680. Line 680 prints the same messages that lines 660 and 670
did, except in all uppercase letters to reflect the proper character mode:

680 PRINT TAB(7) "keyboard diagnostic module":PRINT

690 PRINT TAB(2) "character value key combination set"

This lets you change between the two character sets, and the headings reflect
which set is active.
Line 700 then prints a row of dashes beneath the test headings. This row of
dashes is valid for either graphic character set:

700 PRINT TAB(2)"----- - - - - - - - - - - - --":

RETURN

Line 700 then returns the program to the point in the code from which it came
before it branched to this subroutine.
Recall that line 580 checks the key combination's SHIFT mode. If a value of
zero, one, two, or four is not found there, the program branches down to line 710:

710 GOSUB 630

 Commodore Care Manual 45

Line 710 is a GOSUB to line 630, which displays the diagnostic headings.
Lines 720 and 730 then print a message and return the program to line 220
to wait for another key to test:

720 PRINT" An illegal shift code was encountered!"

730 PRINT "your keyboard needs service" GOTO 220

This message probably indicates a problem with the keyboard. Refer to

"Troubleshooting and Repair Guidelines" earlier in this chapter to help pinpoint
the problem.
Line 740 begins the subroutine to exit the Keyboard Diagnostic Module and
return to the System Diagnostic Main Menu. Line 740 is a POKE statement, poking
a value of 23 into memory location 53272:

740 POKE 53272,23:PRINT "{BLUE}"GOTO 50

This resets the system to graphic set 2, for the upper/lowercase character mode.
This ensures that when the program does return to the Main Menu, all the menu
choices will be displayed in the proper type style.
That's the first part of the exit "housekeeping" routine. The second part prints
CHR$(154) to return the screen color to the default of light blue, in case the user
has been testing the different color commands as part of the keyboard test.
Finally, the GOTO statement returns the program to line 50, which is the
beginning of the System Diagnostic Main Menu.

C128 USERS: Line 740 is modified in the C128 code for a different POKE
location and value.
 Chapter 3
Tile Manitor
When working with a computer, constant visual feedback, or output is necessary.
You need to see your input as you enter it, and you want to see processing results
as the computer produces them. Just as the keyboard is the primary input device,
the computer uses the monitor to provide the primary output.

DESCRIPTION AND FUNCTION OF THE MONITOR

The monitor is also known as a cathode ray tube (CRT) or video display. It
is the screen on which you see the status of the program you're using.
All monitors used with the Commodore can display the two Commodore
graphic character sets. Each set consists of 256 characters, and the sets are used
one at a time. The television-set monitor accommodates 40 characters on each
of 25 I ines at a time (40 x 25 format), for 1000 on-screen character locations. All
other monitors used with the Commodore accommodate 80 characters per line,
with 25 lines per screen (80 x 25 format), for a total of 2000 on-screen character
locations (Fig. 3-1).

Types of Monitors
There are several types of monitors that can work with your Commodore
system. These include the following:

D television set monitors (color or black-and-white)

46
 Commodore Care Manual 47

Fig . 3-1. The 80-column by 25-line screen format.

o monochrome monitors
o high-resolution monochrome graphics monitors
o high-resolution color graphics monitors

The monitor you obtain to work with your Commodore must be able to conform
to the Commodore's RGB (red-green-blue) cable plug. Most computer monitors
available can accommodate this type of cable.

The Television Set Monitor. The, Commodore 64 and 128, like many other
home computers, are designed to use a television set as the monitor. An external
radio frequency (RF) converter is attached to the television via the television's
VHF antenna leads (Fig. 3-2). If your television is cable-ready, you can use a coaxial
cable connector instead of the antenna leads.
The Commodore cable attaches from the back of the Commodore to the RF
converter. The RF converter includes a switch to let you choose between using
the television as a computer monitor ("COMPUTER") and using the television
to view broadcasts (" TV"). There is also a switch on the Commodore that allows
selection of either Channel 3 or Channel 4 as the channel used for the computer
mode.
The television-set monitor can display graphics and color, but only in the
40 x 25 text format (instead of the 80 x 25 text format on a standard computer
monitor) .
48 The Monitor

Fig. 3-2. RF converter attached to television.

The High-Resolution Graphics Monitor. The Commodore high-resolution

graphics monitor illuminates every speck of light, or pixel picture element, in
different combinations to form pictures. These pixels allow you to create and
display computer drawings and graphics on the screen.
The greater the number of pixels, the better the screen resolution. The better
the screen resolution, the sharper the displayed image. This is why the different
types of high-resolution monitors are classified by the actual number of horizontal
and vertical pixels they can accommodate on the screen at one time. The
Commodore graphics monitors accommodate 320 x 200 pixels.

The Color Monitor. The color monitor is a high-resolution monitor that can
display the pixels in different colors. A color monitor can be a vital asset when
using your computer to do business graphics or design work.
If you Jre using a color television as the computer monitor, colors are already
available to you. Another option is to buy a high-resolution color computer mon-
itor that can be used with the special Commodore five-pin composite video port.

How the Monitor Functions

The monitor consists of the cathode ray tube, the power supply, and the
contrast, brightness, and vertical/horizontal hold adjustments. The CRT is a large
vacuum tube with a viewing face similar to a television screen. The electron beam
is focused and controlled to contact the back of the picture tube, which is coated
with a material called phosphor. As the electrons strike the phosphor atoms, the
atoms begin to glow. This reaction serves to form a small, clearly defined light
spot (Fig. 3-3).
A number of these light spots are the dots that form the characters. On a mono-
 Commodore Care Manual 49

Electron Beam ~
----I- Image Produced by
the Electron Beam
...... ....................................
"

~
t
Electron Gun _ _

Fig. 3-3. Electron beam and display image.

C Front of the Screen

chrome monitor, about seven of these light spots make up one character. On a
high-resolution monitor, these light spots are the pixels which vary in density to
form the characters, graphic elements, and drawings.
When a character on the keyboard is pressed to be displayed on the moni-
tor, or when a particular application displays processing results, the program
instructs the monitor to paint a certain pattern which forms the character
representation. The specific pattern displayed is dependent upon the type of display
matrix your monitor has.
When in the text mode, the monitor's display works on a character matrix.
The display is divided into 25 horizontal rows. These rows are intersected by 40
to 80 vertical columns. The position at which a column and row intersect is one
character location (Fig. 3-4).
The high-resolution, or color, display is a matrix as well, but a much more

2 3 4 5 6 7 8 9 10 11 12 13 14 . 80

T H I S I S L I N E I

2
3
4 V~
5 /
6 1/
7 l/
8 V

24
Fig. 3-4. Column/row matrix.
50 The Monitor

precise one, working at a pixel level rather than a character level. Because an
individual pixel is much smaller than a character, and because there is a greater
density of pixels, there is more flexibility and precision represented on the display.
This creates a sharper picture with higher resolution.

Character Generators. A character generator is a part of the system's read-

only memory (ROM) which actually produces the series of pixel ON and OFF
representations, or bit map. Character generators create the characters that are
accessed either through the keyboard or through a program. The Commodore
system employs two character generators, because there are two character sets
available. These character generators are typically accessed whenever you are
working within a text mode such as a word processing application.
The two character sets can only be used one at a time. You can move be-
tween the two character sets by pressing the SHIFT and c~ key simultaneously.
Character set 1 is the uppercase-only character mode. Character set 2 is the
upper/lowercase character mode. Each of these character sets also have special
graphic characters available. Refer to Chapter 2 for more information about
access i ng these graph ic characters from the keyboard.

The Monitor Interface. The Commodore systems have two types of monitor
interfaces available. The one you use depends on whether you're using a television
or a computer monitor.
When using a television as your monitor, a round single-pin cable is used
together with an RF converter to create the monitor interface. One end of this
cable connects into the Commodore system unit, and the other end connects to
the RF converter, which in turn connects to the VHF antenna terminals on the
back of the television (see Fig. 3-2). The RF converter takes the computer's digital
signals and converts them into the analog signals required by the television. In
effect, the computer is functioning as a transmitting station to the television. When
using a computer monitor instead of a television, the round five-pin RGB cable
supplied with the monitor is the monitor interface.

Sprites. A very powerful feature of the Commodore systems is the ability to

define special graphic shapes, called sprites. A sprite is a special display function
in which a particular pattern or design can be described, and the image can be
moved around the screen with very little programming. Up to eight of these sprites
can be used at one time. These sprites are often used in games to represent quickly
moving objects.
Special circuitry, referred to as sprite registers, is built into the Commodore
system unit to control the sprites. A register is a specialized location within memory
used for one particular function, distinct from the main system memory. Registers
make it easy to move the sprites, as well as detect collisions, in which two or
more sprites occupy one or more common pixel locations on the screen. Because
special dedicated hardware handles these functions, the sprites move very quickly
when viewed on the screen. This facilitates high-quality Commodore games, even
when simply programmed with BASIC.
 Commodore Care Manual 51

TROUBLESHOOTING AND REPAIR GUIDELINES

This section describes problems that can occur with the monitor, how to
troubleshoot them, and how to fix them. Many of the troubleshooting steps include
running the Monitor Diagnostic Module. Further instructions and explanations
of this module are provided in the next section, entitled "Running the Diagnostic
Module."

Problem: Nothing Displays on the Monitor

The first major problem is when the monitor does not work at all; when
nothing displays on the screen at all.

[.-j Solutions

D Check the brightness and contrast knobs, and make sure they are turned at
least two-thirds of the way up. Someone else might have turned the controls
down to prevent the screen from etching (see the next section on "Etching").

D Check that the monitor itself is properly connected. If the monitor is a television
set plugged into a different socket than the computer itself, check to see whether
the plug is controlled by a light switch. If it is, turn the light switch on.

D Make sure that the plug is active and working. Test this by plugging another
electrical device into the socket to see if it works. If it does not, an electrical
supply problem is indicated. Check the fuse box or circuit breaker.

D Check the cabling to ensure that the monitor is properly attached to the display
interface of the system unit.

D When the monitor is properly warmed up (it takes a minute or so), turn the
brightness control knob up as far as it wi II go. A series of lines shou Id be
displayed across the screen (Fig. 3-5). If you don't see this, and the screen
remains blank, then the monitor's power supply might be defective. Take the
monitor in for servicing.

D If the monitor is making a crackling noise and the screen remains blank, this
might indicate a problem with the display interface. If you run your hand next
to the screen, the hairs on the back of your hand might become attracted to it.

Fig. 3·5. High brightness lines.

52 The Monitor

First, try swapping a different monitor or television onto your system. If this
monitor works, then your other monitor needs servicing. If the swapped monitor
does not work either, a problem with the system unit itself is indicated. Refer
to Chapter 2 for system unit troubleshooting procedures.

Problem: StatIc on the TelevIsIon Screen

A problem with static is related to the previous problem of having nothing
display on the screen. If you are working with a television monitor, and you have
no picture but static, you could have a problem with the television set, the RF
converter, or the computer system unit.

[2] SolutIons

D First check the television. To do this, switch the RF converter to the television
mode, or disconnect it altogether. Then change the television channel to a
known working station. For example, if you know that you receive Channel
2 very well, turn it to Channel 2. If you still do not receive Channel 2 nor
any other channel, there is a problem with the television's tuning or receiving
mechanism, and it should be taken in for servicing.

[J If there is a television picture, then you know that the television is working
fine, and you should test the RF converter. The RF converter has two switch
positions: COMPUTER and TV. Make sure that the converter is switched to
the COMPUTER position. Check that the converter is properly connected to
the correct antenna leads: VHF rather than UHF.
Next, make sure the channel selector is set properly for the computer.
The Commodore is set up so that it can operate from either Channel 3 or
Channel 4. Select which channel the computer will use with the slide switch
on the rear of the Commodore system unit/keyboard. The channel selected
on the computer should be the channel the television is on.
If the screen still shows just static, replace the RF converter. You can obtain
one for approximately $5 at a stereo or electronics store.
[J !f you try a!! the previous solutions with thp tplevision 5Pt ;mrl thp RF ronvprtpr,
but there is still static on the television screen, the computer system unit is
probably having a problem. Refer to Chapter 2, "The System Unit/Keyboard"
to troubleshoot system unit problems.

Problem: EtchIng
Etching, or ghosting, takes place on the screen when one particular format,
such as the text editor menus or database screen, is displayed on the screen for
long periods of time without changing. If the computer is left running with the
same image displayed for many hours a day, or many days a week, the constant
bombardment of the electrons on the same area of the picture tube phosphor can
permanently burn, or etch, that image into the screen. When that happens, even
when something else is displayed, you will still see a ghost image of the etched
 Commodore Care Manual 53

display. At the same time, the display you want to see will be fainter, more
"washed out."
There isn't anything you can do to make an image that is etched into your
display go away. In other words, you can't "fix" etching, unless you buy a new
monitor. The key in this case is prevention. To prevent etching, either turn off
the display or turn down the brightness when the computer is not in use.

Problem: Blank Character Location

Depending on the type of monitor you use, characters are displayed either
in a character or a pixel matrix. A problem can occur in which one of these
character locations in the matrix does not display anything; a character is entered
to be placed at a certain location, but the character does not display.
The high-resolution display is based on the pixel matrix, with the display
divided by a large number of pixels, giving the screen its high-resolution attributes.
This creates a very fine matrix, so rather than the character being the smallest
unit that can display on the monitor, the pixel is the smallest unit. The problem
might be that pixels are not displaying. Certain characters might be missing, which
happens when the computer has lost a particular memory location. You might
also see a part of a character missing, or even intermittent spots on the display,
looking like pin pricks poked into the screen.

2] Solution

o To troubleshoot this problem, run the Display Test of the Monitor Diagnostic
Module. Press a character on the keyboard, and the entire screen should be
filled with this character at every available character location. If you see that
a particular character is missing, there is a problem in the display interface
board. Each character represents a video memory location. If a character does
not display, it means that its memory location is probably bad, and chips need
to be replaced. Take the CPU board in for servicing.

Problem: Misaligned Display

Even if you are using a computer monitor instead of a television for your vis-
ual display, you can still have the same types of problems that can occur with
a television. For example, the picture can become skewed, or it can appear
compressed. It can also go out of alignment (Fig. 3-6).

II I
Fig 3-6. Misaligned displays.
54 The Monitor

In many cases, it is more difficult to perceive such alignment problems when

there is nothing but text on the screen. To check for proper alignment, try the
following solutions.

~ Solutions

D Run the Alignment Test. If the grid does not appear square and symmetrical
on the screen, the monitor needs adjustment. There are adjustment
potentiometers on the back of most monitors. Use the tuning wand (do not
use a metal screwdriver!) to gently turn these potentiometers ("pots") either
clockwise or counterclockwise to bring the screen back into alignment. Note
the direction you're turning the pot, and make only one-quarter of a turn at
a time, so you can easily return the pot to its original position if necessary.

D If adjusting the pots does not bring the monitor back into the proper alignment,
take the monitor in for servicing and have it adjusted.

D If your monitor is a television set, simply adjust the horizontal and vertical
hold controls until the alignment grid looks straight.

Problem: A Particular Character Does Not Display

If you press a character key on the keyboard, but do not see it displayed on
the monitor, there is probabiy a problem with the character generator ROM.

~ Solution

D If you run the Display Test and do not see all the expected characters, or if
the display is incorrect or garbled, a problem with the system unit itself is
indicated. Refer to Chapter 2, "The System Board/Keyboard" to troubleshoot
the system unit.

Problem: Colors Do Not Display Correctly

When using a color monitor (either the color television or a high-resolution
color monitor), another problem you could encounter is that no colors display
at all, or that the colors display the incorrect tones. Check the colors with the
Color Test of the Monitor Diagnostic Module. The screen displays the names of
the colors, then displays bars of color in the appropriate shades. If the color names
and the actual colors do not match, there is a monitor color problem.

~ Solutions

D First make sure that the monitor is actually a color television or a color moni-
tor instead of a black-and-white television or monochrome monitor.

D If the monitor is displaying colors, but they're not the correct colors, there
are two different adjustments you can make to rectify this problem.
If you're using a television monitor, first check a normal television picture,
 Commodore Care Manual 55

and see if that color is adjusted properly. If the picture doesn't look right, for
instance, if faces look too red , or green, then you simply need to adjust the
color and tint controls on the television set.
Once the television broadcast picture has displayed the correct colors,
switch the television back to the computer mode and check the color. It's
possible that the color of a television broadcast might look fine, but when
working in the computer mode, the colors are wrong and/or fuzzy. \Vhen work-
ing with a computer monitor, you can simply adjust the color and tint controls
of the monitor, just as you would with a televi sion.
o After making the proper adjustments, if the colors are still not correct, you'll
need to adjust a variable resistor inside the computer's system unit on the
motherboard. To do this, first remove the cover to the system unit, following
these steps:
1. Turn the system off and disconnect all peripheral cables.
2. Turn the system unit upside-down, resting the keyboard on foam or pa-
per to protect it.
3. Remove the three phillips-head screws (Fig. 3-7).
4. While holding the case together, place the system unit keyboard-side up
again .
5. Grasp the case on the bottom edge (by the SPACE BAR) and I ift. The case
is hinged and will fold back. Do this slowly and carefully to avoid
jerking the keyboard cable from its connector.
6. Carefully bend back the silver ca rdboard cover which shields the
motherboard (Fig. 3-8).
Now adjust the color trim. To do this, follow these steps:

Fig. 3-7. Removing the system unit screws.

56 The Monitor

Fig. 3-8. Opening the system unit.

1. Reconnect the power supply, monitor, and disk or cassette drive.

2. Turn the system power on. While the system is open and powered-on,
do not touch anything, and when making adjustments, use only a
nonconductive (plastic) tuning wand. Do not use a metal screwdriver.
3. Load and run the System Diagnostic Program. Choose the Monitor
Diagnostic, and then the Color Test within that diagnostic (refer to "Run-
ning the Monitor Diagnostic Module" later in this chapter for further
instructionsl-
4. Prop up the upper part of the system unit case in order to expose the
motherboard.
5. Locate the color trim variable resistor on the motherboard (Fig. 3-9).
6. Use your tuning wand (do not use a metal screwdriver) to adjust this
resistor until you see satisfactory colors on the screen display.
Finally, close up the computer. To do this, follow these steps:
1. When the colors look correct, turn the system off again and disconnect
the peripheral cables.
2. Replace the silver cardboard shield in its place over the motherboard.
3. Bring down the top cover of the system unit.
4. Holding the case together, turn the system unit upside-down. Again,
protect the keyboard with a foam pad.
5. Replace the three phillips screws.
6. Turn the system unit keyboard-side up again, and connect all the peripheral
and power supply cables.
7. Power up the system and run one or two passes of the Exerciser program
(see Chapter 8, "The Exerciser") to ensure that the system is function-
ing properly.
 Commodore Care Manual 57

Rear

D
Motherboard
o
o
c:J
c:JC

Color trim
resistor

Front

Fig. 3-9. Adjusting the color trim resistor.

Adjusting the color from inside the system unit does not affect the color and
tint settings of the television or the monitor whatsoever.

Problem: Monitor Does Not Scroll Properly

When the screen is completely filled with text and you enter more characters
on the next line, the entire screen moves itself up, pushing the top line off the
screen, making place for the next line. This is called scrolling.
If the display does not move up, but rather fills one screen and then overwrites
at the bottom of the screen, the monitor has a scrolling problem.

B Solution

o To check the scrolling, run the Scroll Test. Enter enough repetitions, about
30, so that the printed lines will more than fill up the screen. if the display
does not scroll properly, then there is a problem with the display section of
the system unit. Refer to Chapter 2 and troubleshoot the system unit.

Problem: Sprites Do Not Display Correctly

There are eight sprites available for use primarily as quickly moving objects
in games. A problem that can occur is that one of these eight sprites might not
be working properly. There is a sprite register for each one of the sprites in the
58 The ,'IdnnJtor

display sectioll of memory. A problem with the sprite memory register could cause
a problem with the sprite display.
You might susiJect a sprite problem when running a game, for example, if
olle of the objects do not rnove or look quite right. Confirrn the problem by run-
ning the Sprite Test of the Monitor Diagnostic Module.

!;.;; Solution

If the sprite doe" not move, or if it rs the wrong color (it should be white)
or the wrong shape (it should be a square), there is a problem with the sprite
circuitry in the system unit. If this is the case, refer to Chapter 2 and troubleshoot
the system unit.

RUNNING THE MONITOR DIAGNOSTIC MODULE

To run the i\klllitor Diagnostic Module, follow the instructions provided in
"Running the Diagnostic Program" in Chapter 1. Then press M. The screen clears,
and the Monitor Diagnostic Menu is displayed (Fig. 3-10). To activate one of these
tests, press the corresponding number. To end the Monitor Diagnostic Module,
press the ESC key. The Diagnostic Main Menu will be displayed again.

Display Test
To run the Display Test, press 1. The screen clears and then gives the test
instruction (Fig. 3-11). Press d character on the keyboard. (Function keys and the

/'
Monitor Diagnostic

1 ... Display Test

2 ... Alignrnent Test

3 .. . Character Set Test

4 ... Color Test

5 ... Scroll Test

6 ... Sprite Test

Press CLR/HOME to End Diagnostic

 Commodore Care Manual 59

Display Test

Press Any Character to Fill Screen

Press CLR/HOME to End Test

Fig. 3-11. Display Test instructions.

cursor arrow keys do not work for this test, because they do not have a particular
graphic display.) The character fills the entire screen at every available character
location, including the status line.
At this point, any character locations that do not display the character, or any
pixels that are "out," are suddenly very obvious.
After displaying the character at every location, the program waits for you
to press another character. You may enter another character at this point, or press
CLR/HOME to return to the Monitor Diagnostic Menu.
Both character sets, set 1 and set 2, can be used for this test. It's a good idea
to run the Display Test twice, once for character set 1, and again for set 2.
The Display Test can also be used to validate a keyboard problem. Because
the Keyboard Diagnostic relies on user input to display a character, a faulty key
might not produce a particular character. If the Keyboard Diagnostic indicates
a problem, check it again with the Display Test. The Display Test generates the
characters by using a program, so if there is a character in this test that you did
not see in the Keyboard Test, this confirms a keyboard problem. Refer to Chapter
2 to troubleshoot the keyboard.

Alignment Test
Pressing 2 from the Monitor Menu presents the Alignment Test, which displays
the alignment box with horizontal and vertical lines resembling Fig. 3-12.
The alignment grid helps you look for any alignment or skew problems. The
display should look symmetrical, with straight lines and no distortion. To end
this test and return to the Monitor Diagnostic Menu, press any key on the keyboard.
60 The Monitor

ALIGNMENT TEST

PRESS ANY KEY TO END TEST

Fig. 3-12. Alignment Test results

Character Set Test

Press 3 to invoke the Character Set Test. This test checks whether any
characters are missing.
You are prompted to enter the character set to be tested, set 1 or set 2. \Vhen
you make the choice, the Character Set Test places all 256 display characters of
that set (Fig. 3-13) on the screen. Pressing any key ends this test and displays the
Monitor Diagnostic Menu again.

Color Test
To test color on a color monitor, press 4 from the Monitor Diagnostic Menu.
The screen displays the name of the color, then a bar of that color (see Fig. 3-14).
All the colors available for your monitor are displayed in this manner.
This test is particularly useful not only to test the colors of the monitor, but
also to adjust the colors if there is a problem with them. Leave this test displayed
on the screen, and make the necessary adjustments, until all the colors look right.
Refer to "Troubleshooting and Repair Guidelines" earlier in this chapter for the
adjustment procedure.
When you press any key, the Color Test is cleared, and the Monitor Diagnostic
Menu is displayed again.

Scroll Test
To test scrolling and scroll rates, press 5 from the Monitor Diagnostic Menu.
The Scroll Test prompts for the number of repetitions for the test. Enter a number
 Commodore Care Manual 61

Character Set Test

Enter Character Set <i) or· (2)-

• "" $ %:&' () * +, -. /0 1234:5 6 789:; < D)? 15!. b e d . f g
h~JKlmnopqr:s.tuvw)(YZ[f:.]t"-ABCOEFGHlJKL..MNO
PQRSTUVWXYZ+I 1:::::\);J .... IiI;JUY~.!IIIIIIIIIIIIII!!I:: 1.-_1"
I _:9. I ... • L , _ r ...1. • --1 I I I - - _. • • -l • . . - h B C. u E F G H 1 J K L t·t N
OPQRSTUVWXYZ+( I::'<~ 1 . - _ 1 . I .. ~ 1 f - . L , _ r . . . L T --111 I
--_)I".-.J ~~

Fig. 3-13. Character Set Test results.

Color Test
Black XXXXXXXXXXXXXXXXXXXX
White XXXXXXXXXXXXXXXXXXXX
Red XXXXXXXXXXXXXXXXXXXX
Cyan XXXXXXXXXXXXXXXXXXXX
Purple XXXXXXXXXXXXXXXXXXXX
Green XXXXXXXXXXXXXXXXXXXX
Blue XXXXXXXXXXXXXXXXXXXX
Yellow XXXXXXXXXXXXXXXXXXXX
Orange XXXXXXXXXXXXXXXXXXXX
Brown XXXXXXXXXXXXXXXXXXXX
Light Red XXXXXXXXXXXXXXXXXXXX
Gray 1 XXXXXXXXXXXXXXXXXXXX
Gray 2 XXXXXXXXXXXXXXXXXXXX
Light Green XXXXXXXXXXXXXXXXXXXX
Light Blue XXXXXXXXXXXXXXXXXXXX
Gray 3 XXXXXXXXXXXXXXXXXXXX
press any key to end test
Fig. 3-14. Color Test results.
62 The Monitor

greater than 25 so that you will indeed see scrolling take place. The test displays
the same line over and over again in a "sliding" character set display on the screen.
It will display the number of lines that you have specified.
Once the screen is filled, the top line scrolls off the top of the screen and
disappears, while a new line appears at the bottom of the screen. If new lines
are added to the bottom, the lines of the character set appear to "walk" or slide
sideways, one character at a time. If it scrolls properly, the screen will resemble
Fig. 3-15.

Sprite Test
The Sprite Test is accessed by pressing 6 from the Monitor Diagnostic Menu.
The first sprite appears at the left edge of the screen and moves to the right edge.
Each of the eight sprites appear in succession, one at a time.
The sprites are represented by a white square (Fig. 3-16). If you do not see
a sprite appear, if its movement is erratic, or if it is the wrong color or shape,
there is a problem in the sprite-handling logic of your cpu. Refer to Chapter 2
and troubleshoot the system unit.
When monitor testing is complete, press CLR/HOME to return to the System
Diagnostic Main Menu.

HOW THE MONITOR MODULE WORKS

Selecting M (or m) from the System Diagnostic Main Menu causes the program
to branch to line 800, which is the start of the Monitor Diagnostic Module (Fig.
3-17).

Scrull Test

Enter the Number of Repetitions-35

! "# $ %&" ( ) * + , / 0 12 3 456789: ; < = > ?@ABCDEFGH I
!"#$%&"()*+,/0123456789:;<=>?@ABCDEFGHI
"#$%&" () *+, /0123456789:; <=>?@ABCDEFGHI !
#$%&"()*+,/0123456789:;<=>?@ABCDEFGHI !"
$%&"()*+,/0123456789:;<=>?@ABCDEFGHI !"#
%&" () *+,/0123456789: ;<=>?@ABCDEFGHI ! "#$
&"()*+,/0123456789:;<=>?@ABCDEFGHI !"#$%
" ( ) * + , / 0 123456789 : ; < = >?@ABCDEFGH I !" # $ %&
( ) * + , / 0 12 3 4 5 6 7 8 9: ; < = > ?@ABCDEFGH I !" # $ %&"
) *+, /0123456789: ; <=>?@ABCDEFGHI ! "#$%&" (
*+, /0123456789:; <=>?@ABCDEFGHI ! "#$%&" ()
+, /0123456789: ; < =>?@ABCDEFGHI ! "#$%&" () *
, /0123456789:; <=>?@ABCDEFGHI ! "#$%&" () *+
/0123456789:; <=>?@ABCDEFGHI ! "#$%&" () *+,
0123456789:;<=>?@ABCDEFGHI !"#$%&"()*+,/
123456789:; <=>?@ABCDEFGHI ! "#$%&" () *+, /0
23456789:;<=>?@ABCDEFGHI !"i/$%&"()*+,/Ol
3456789:;<=>?@ABCDEFGHI !"#$%&"()*+,/012
456789:;<=>?@ABCDEFGHI !"#$%&"()*+,/0123
56789:; <=>?@ABCDEFGHI ! "#$%&" () *+, /01234
6789: ;<=>?@ABCDEFGHI ! "#$%&" () *+, /012345
789:; <=>?@ABCDEFGHI ! "#$%&" () *+, /0123456

Fig. 3·15. Scroll Test results.

 Commodore Care Manual 63

Sprite Test

-
,- -,
-

Fig. 3·16. Sprite Test results.

Line 800 goes first to the Clear Screen subroutine at line 2990. The REMARK
statement indicates that this is the Monitor Diagnostic Module:

800 GOSUB 2990:REM "Monitor Diagnostic Module"

Six tests are included in the Monitor Diagnostic Module. Lines 810 through
880 print the test selection menu on the screen:

810 PRINT TAB(6) "Monitor Diagnostic":PRINT

820 PRINT TAB(5) "1 ... Display Test":PRINT
830 PRINT TAB(5) "2 ... Alignment Test":PRINT
840 PRINT TAB(5) "3 ... Character Set Test":PRINT
850 PRINT TAB(5) "4 ... Color Test":PRINT
860 PRINT TAB(5) "5 ... Scroll Test":PRINT
870 PRINT TAB(5) "6 ... Sprite Test":PRINT

Line 890 instructs the user to press the CLRiHOME key when they want to quit
the Monitor Diagnostic and return to the System Diagnostic Main Menu:

890 PRINT TAB(5) "Press CLR/HOME to End Diagnostic"

Line 900 sends the program to the Get-a-Key subroutine at line 3000:
64 The Monitor

800 GOSUB 2990:REM "Monitor Diagnostic Module"

810 PRINT TAB(6) "Monitor Diagnostic":PRINT
820 PRINT TAB(5) "1 ••. Display Test":PRINT
830 PRINT TAB(5) "2 •.• Al ignment Test":PRINT
840 PRINT TAB(5) "3 ... Character Set Test":PRINT
850 PRINT TAB(5) "4 ... Color Test":PRINT
860 PRINT TAB(5) "5 ..• Scroll Test":PRINT
870 PRINT TAB(5) "6 ... Sprite Test":PRINT
890 PRINT TAB(5) "Press CLR/HOME to End Diagnostic"
900 GOSUB 3000
1000 IF ASC(A$)=19 THEN 50
1010 iF A$="1" THEN 1090
1020 IF A$="2" THEN 1180
1030 IF A$="3" THEN 1320
1040 IF A$="4" THEN 1440
1050 IF A$="S" THEN 1650
1070 IF A$="6" THEN 1770
1080 GOSUB 3100:GOTO 900
1090 GOSUB 2990:REM Display Character Set Test
1100 PRINT TAB(14) "Display Test":PRINT
1110 PRINT "Enter Any Character to Fill Screen":PRINT
1120 PRINT "Press CLR/HOME to End Test"
1130 GOSUB 3000
1132 PRI NT "(CLR/HCloIE)"
1135 IF ASC(A$)=19 THEN 800
1140 FOR 1=1 TO 999
1150 PRINT A$; :NEXT
1155 IF EX=1 THEN 1360
1160 GOTO 1130
1180 GOSUB 2990:REM Alignment Test
1185 POKE 53272,21
1190 PRINT TAB(13) "al igrrnent test":
1200 PRINT CHR$(176);:FOR 1=1 TO 18: PRINT CHR$(99);:NEXT
1210 PRINT CHR$(178);:FOR 1=1 TO 18: PRINT CHR$(99);:NEXT
1220 PRINT CHR$(174):
1230 FOR 1=1 TO 10: PRINT CHR$(98);TAB(19)CHR$(98);
TAB(38)CHR$(98):NEXT I
1240 PRINT CHR$(171);:FOR 1=1 TO 18 PRINT CHR$(99);:NEXT
1250 PRINT CHR$(123);:FOR 1=1 TO 18 PRINT CHR$(99);:NEXT
1260 PRINT CHR$(179)
1270 FOR 1=1 TO 10:PRINT CHR$(98);TAB(19) CHR$(98);TAB(38)
CHR$(98):NEXT
1280 PRINT CHR$(173);:FOR 1=1 TO 18:PRINT CHR$(99);:NEXT
1290 PRINT CHR$(177);:FOR 1=1 TO 18:PRINT CHR$(99);:NEXT

Fig. 3-17. The Monitor Diagnostic Module listing.

 Commodore Care Manual 65

1300 PRINT CHR$(189):GOSUB 3200

1310 POKE 53272,23:GOTO 800
1320 GOSUB 2990:REM "Character Set Test"
1330 PRINT TAB(11) "Character Set Test"
1340 PRINT:PRINT "Enter Character Set (1) or (2)-"
1350 GOSUB 3000
1360 IF A$="1" THEN POKE 53272,21
1370 FOR 1=32 TO 255
1380 IF 1=128 OR 1=130 OR 1=131 OR 1=132 OR 1=141
1=143 OR 1=144 THEN 1410
1390 IF 1=145 OR 1=146 OR 1=147 OR 1=148 O~ 1=156
OR 1=157 OR 1=158 THEN 1410
1395 IF 1=159 THEN 1410
1400 PRINT CHR$(I);+" ";
1410 NEXT
1415 IF EX=1 THEN POKE 53272,23:GOTO 1440
1420 PRINT:GOSUB 3200
1430 POKE 53272,23:GOTO 800
1440 GOSUB 2990:REM "Color Test"
1450 PRINT TAB(15) "Color Test":PRINT
1460 "C$="XXXXXXXXXXXXXXXXXXXX"
1470 PRINT "{CTRL 1} Black";TAB(12) C$
1480 PRINT "{CTRL 2} IoIhite";TAB(12) C$
1490 PRINT "{CTRL 3} Red";TAB(12) C$
1500 PRINT "{CTRL 4} Cyan";TAB(12) C$
1510 PRINT "{CTRL 5} Purple";TAB(12) C$
1520 PRINT "{CTRL 6} Green";TAB(12) C$
1530 PRINT "{CTRL 7} Blue";TAB(12) C$
1540 PRINT "{CTRL 8} Yellow";TAB(12) C$
1550 PRINT "{C= n Orange";TAB(12) C$
1560 PRINT "{C= 2} Brown";TAB(12) C$
1570 PRINT "{C= 3} Lt. Red";TAB(12) C$
1580 PRINT "{C= 4) Gray 1";TAB(12) C$
1590 PRINT "{C= 5} Gray 2";TAB(12) C$
1600 PRINT "{C= 6} Lt. Green";TAB(12) C$
1610 PRINT "{C= 7} Lt. Blue";TAB(12) C$
1620 PRINT "{C= 8} Gray 3";TAB(12) C$
1625 IF EX=1 THEN PRINT "{C= 7)":GOTO 1680
1630 PRINT:GOSUB 3200
1640 PRINT "{C= 7}":GOTO 800
1650 GOSUB 2990:REM "Scroll Test"
1660 PRINT TAB(15) "Scroll Test":PRINT
1670 PRINT "Enter the NLI1ber of Repetitions-";A:PRINT
1680 N=31
1690 FOR 1=1 TO A

Fig. 3-17. The Monitor Diagnostic Module listing. (Continued from page 64.)
66 The Monitor

1700 N=N+1:IF N>71 THEN N=32

1710 FOR X=1 TO 40
1720 PRINT CHR$(N);:N=N+1
1730 IF N>71 THEN N=32
1740 NEXT X
1750 NEXT I
1755 PRI NT
1757 IF EX=1 THEN 1770
1760 GOSUB 3200
1765 GOTO 800
1770 GOSUB 2990:REM "Sprite Test"
1780 PRINT TAB(15)"Sprite Test"
1790 FOR S=2040 TO 2047:POKE S,13:NEXT
1792 FOR S=832 TO 894:POKE s,255:NEXT
1800 V=53248:PQ(E V+21,255
1810 FOR S=39 TO 46:POKE V+S,1:NEXT S
1815 R=O
1820 FOR 1=0 TO 7
1830 POKE 53269,PEEK(53269)OR(2tl)
1840 FOR X=24 TO 255
1850 POKE (V+I*2),X:POKE (V+I*2+1),152
1860 NEXT X
1870 POKE (V+16),R(I)
1880 FOR X=O TO 65
1890 POKE (V+(1*2»,X:POKE (V+(1*2+1»,152
1895 NEXT X
1897 POKE V+16,PEEK(V+16)AND 254
1900 POKE 53269,PEEK(53269)AND(255-2tl)
1910 NEXT I
1915 IF EX=1 THEN RETURN
1920 PRINT:GOSUB 3200
1930 GOTO 800

Fig. 3-17. The Monitor Diagnostic Module listing. (Continued from page 65.)

900 GOSUB 3000

When the user presses a key, its value is placed into variable A$. Line 100 checks
whether the value of A$ is equal to 19, which is the CLRiHOME key. If it is, the
program returns to line 50, the beginning of the System Diagnostic Main Menu:

1000 IF ASC(A$) = 19 THEN 50

If the value of A$ is not equal to 19, lines 1010 through 1070 check to see whether
the key pressed is a valid entry for this test, valid entries being numbers 1 through
6. If the user pressed a 1 for the Display Test, the program would branch to line
1090. If the user pressed 2 for the Alignment Test, the program would branch
to line 1180, and so on:
 Commodore Care Manual 67

1010 IF A$= "1" THEN 1090

1020 IF A$="2" THEN 1180
1030 IF A$="3" THEN 1320
1040 IF A$= "4" THEN 1440
1050 IF A$="5" THEN 1650
1070 IFA$="6" THEN 1770

If the user does not press a valid key, the program falls through to line 1080. Line
1080 sends the program to the Beep subroutine at line 3100 to signal the error.
The program returns, then goes back to line 900 to let the user try again with
another key:

1080 GOSUB 31 00 GOTO 900

Line 1090 is the beginning of the Display Test. It goes to the Clear Screen
subroutine at line 2990. The REMARK statement indicates that this is the Display
Test:

1090 GOSUB 2990:REM Display Character Set Test

Lines 1100 through 1120 display the Display Test title and prompts on the screen:

1100 PRINT TAB(14) "Display Test":PRINT

1110 PRINT "Enter Any Character to Fill Screen":PRINT
1120 PRINT "Press CLR/HOME to End Test"

The program falls through to line 1130, which goes to the Get-a-Key subroutine
at line 3000. When the user presses a key, the program returns to line 1132:

1130 GOSUB 3000

Line 1132 prints the CLRlHOME key, which clears the screen to prepare for the
actual test:

1132 PRINT "{CLR/HOME}"

Line 1135 checks whether the ASCII value of A$ is 19, the CLRlHOME key. If it
is, the program branches back to line 800 to display the Monitor Diagnostic Menu:

1135 IF ASC(A$) = 19 THEN 800

If the key is not the CLRlHOME key, the program falls through to line 1140. This
I ine begins a FOR-TO loop which runs from 1 through 999 for the number of
characters needed to fill up the screen display:

1140 FOR I = 1 TO 999

68 The Monitor

The program falls through to line 1150, which prints the value contained in A$,
obtai ned from the Get-a-Key subroutine when the user pressed a key. It also
includes the N EXT statement which loops the program back to line 1140 for 999
iterations:

1150 PRINT A$;NEXT

Line 1155 checks whether the Exerciser Module is in effect. If EX is set to one,
the program branches to the next test. If EX is equal to zero, the program falls
through to the next line.

1155 IF EX=1 THEN 1360

Line 1160 branches back to line 1130 to wait for another keystroke. The program
continues to display any key pressed until the user presses the CLRlHOME key.

1160 GOTO 1130

When the user presses 2 trom the Monitor Diagnostic Menu, the program branches
to the Alignment Test starting at line 1180.
Line 1180 uses the Clear Screen subroutine to prepare the screen for this test.
The REMARK statement indicates the test name:

1180 GOSUB 2990:REM Alignment Test

Line 1185 sets the mode to the uppercase-only character mode. This accesses
the characters necessary to draw the alignment grid for this test.

1185 POKE 53272,21

C128 USERS: Line 1185 in the C128 code reflects a different POKE location
and value.

Line 1190 prints the test title on the screen:

1190 PRINT TAB(13) "alignment test":

Lines 1200 through 1300 paint the alignment grid on the screen. This is done
with FOR-TO loops of the graphic characters which form bins, vertical bars, and
horizontal bars.

1200 PRINT CHR$(176);FOR 1=1 TO 18: PRINT CHR$(99);:NEXT I

1210 PRINT CHR$(178);FOR 1=1 TO 18: PRINT CHR$(99);NEXT I
1220 PRINT CHR$(174):
1230 FOR 1=1 TO 10: PRINT CHR$(98);TAB(19)CHR$(98);
TAB(38)CHR$(98):NEXT I
 Commodore Care Manual 69

1240 PRINT CHR$(171);:FOR 1=1 TO 18 PRINT CHR$(99);:NEXT

1250 PRINT CHR$(123);:FOR 1=1 TO 18 PRINT CHR$(99);NEXT
1260 PRINT CHR$(179)
1270 FOR 1=1 TO 1O:PRINT CHR$(98);TAB(19) CHR$(98);TAB(38)
CHR$(98):NEXT
1280 PRINT CHR$(173);:FOR 1=1 TO 18:PRINT CHR$(99);:NEXT I
1290 PRINT CHR$(177);:FOR 1=1 TO 18:PRINT CHR$(99);:NEXT
1300 PRINT CHR$(189):GOSUB 3200

Once the alignment grid is painted, the program goes to the subroutine at 3200,
which displays a prompt to enter any key to continue. When the user enters a
key, the program returns to line 1310.
Line 1310 resets the character mode to the upper/lowercase mode with the
POKE instruction. It then branches back to line 800, the beginning of the Mon-
itor Diagnostic Module:

1310 POKE 53272,23:GOTO 800

C128 USERS: Line 1310 in the C128 code is modified to reflect a different
POKE location and value.

When the user presses 3 from the Monitor Diagnostic Menu, the program
branches to line 1320 to begi n the Character Set Test. Thi s test provides a display
of the full graphic character set available through the computer's character
generator, either Commodore character set 1 or character set 2.
At line 1320, the Clear Screen subroutine clears the screen. The REMARK
statement indicates the name of the test:

1320 GOSUB 2990 REM "Character Set Test"

Line 1330 displays the test title on the screen:

1330 PRINT TAB(11) "Character Set Test"

Line 1340 prompts the user to indicate which character set is being used for the test:

1340 PRINT:PRINT "Enter Character Set (1) or (2) -"

Line 1350 then branches to the Get-a-Key subroutine at line 3000 to get the
character pressed by the user in response to this prompt. The character is placed
in variable A$, which is used in line 1360:

1350 GOSU B 3000

Line 1360 checks to see if the value of A$ is equal to one. If it is, a POKE reads
into memory location 53272, set to 21, ensuring that the user is set up for the
chosen character set:
70 The Monitor

1360 IF A$="1" THEN POKE 53272,21

C128 USERS: The C128 code at line 1360 is modified to reflect a different
POKE location and value.

Line 1370 does a FOR-TO loop, indicating the range of characters that are
to be displayed for this test:

1370 FOR I =32 TO 255

Lines 1380 through 1395 check for special cursor positioning characters which
would alter the display. When the FOR-TO loop increments to one of these
characters, lines 1380 through 1395 catch it and cause the program to ignore
it by going to the end of the N EXT loop at line 1410. The program then increments
to the next character string value:

1380 IF 1=128 OR 1=130 OR 1=131 OR 1=132 OR 1=141

1=143 OR 1=144 THEN 1410
1390 IF 1=145 OR 1=146 OR 1=147 OR 1=148 OR 1=156
OR 1=157 OR 1=158 THEN 1410
1395 IF 1=159 THEN 1410

If the next character is a valid, displayable character, it is placed in CHR$(I), and

then line 1400 prints it on the screen. A blank space is placed after the character:

1400 PRINT CHR$(I); +" ";

Line 1410 is the NEXT statement which increments the character string value:

1410 NEXT

When all 255 characters have been printed, the program falls through to line
1415, which checks whether the EX exerciser flag is on. If it is set to one, the
program sets the system to the upper/lowercase character mode, and then branches
to line 1440:

1415 IF EX=1 THEN POKE 53272,23:GOTO 1440

C128 USERS: The C128 code at line 1415 is modified to reflect a different
POKE location and value.

Line 1420 then branches to the subroutine at line 3200, which prints the
prompt to enter any key to end test. Once the user enters any key, the program
falls through to line 1430:

1420 PRINT:GOSUB 3200

 Commodore Care Manual 71

Line 1430 POKEs memory location 53272 to 23 to make sure that it's in the
upper/lowercase character mode. The program then returns to line 800, which
is the start of the Monitor Diagnostic Menu:

1430 POKE 53272,23:GOTO 800

C128 USERS: The C128 code at line 1430 is modified to reflect a different
POKE location and value.

When the user enters a 4 from the Monitor Diagnostic Menu, the program branches
to line 1440 for the start of the Color Test.

NOTE: If you do not have a color monitor, you may delete this routine from
the System Diagnostic Program, or simply ignore it.

Line 1440 clears the screen and incl udes the identifying REMARK statement:

1440 GOSUB 2990:REM "Color Test"

Li ne 1450 displays the test title at the top of the screen:

1450 PRINT TAB(15) "Color Test":PRINT

Line 1460 assigns a series of 20 Xs to variable C$. This is used for the color bar
pattern:

1460 "C$="XXXXXXXXXXXXXXXXXXXX"

Lines 1470 through 1620 are PRINT statements that print the name of the
color in that color, and then fills in the blanks in C$ with that color. This is done
for all 16 colors:

1470 PRINT" {CTRl 1} Black";TAB(12) C$

1480 PRINT "{CTRl 2} White";TAB(12) C$
1490 PRINT "{CTRl 3} Red";TAB(12) C$
1500 PRINT" {CTRl 4} Cyan";TAB(12) C$
1510 PRINT "{CTRl 5} Purple";TAB(12) C$
1520 PRINT" {CTRl 6} Green";TAB(12) C$
1530 PRINT "{CTRl 7} Blue";TAB(12) C$
1540 PRINT" {CTRl 8} Yellow";TAB(12) C$
1550 PRINT" {C= 1} Orange" ;TAB(12) C$
1560 PRINT "{C= 2} Brown";TAB(12)C$
1570 PRINT "{C= 3} Lt. Red";TAB(12) C$
1580 PRINT "{C= 4} Gray 1";TAB(12) C$
1590 PRINT" {C= 5} Gray 2";TAB(12) C$
72 The Monitor

1600 PRINT "{C= 6} Lt. Green";TAB(12) C$

1610 PRINT "{C= 7} Lt. Blue";TAB(12) C$
1620 PRINT "{C= 8} Gray 3";TAB(12) C$

Line 1625 checks for the exerciser flag EX once again. If it is set to one, the
color is reset to the default of light blue. Then the program branches to line 1680:

1625 IF EX=1 THEN PRINT "{C= 7}":GOTO 1680

At line 1630, a blank line is printed. The subroutine at line 3200 prompts
the user to enter any key to end the test. This provides the user with ample time
to make any necessary monitor color adjustments:

1630 PRINT:GOSUB 3200

Line 1640 resets the screen to its default of light blue, then the program
branches back to line 800 to display the Monitor Diagnostic Menu:

1640 PRINT "{C= 7}":GOTO 800

When the user presses 5 from the Monitor Diagnostic Menu, the program branches
to line 1650.
Line 1650 clears the screen and identifies the name of the test:

1650 GOSUB 2990:REM "Scroll Test"

Line 1660 displays the test title:

1660 PRINT TAB(15) "Scroll Test":PRINT

Line 1670 prompts the user to enter the number of repetitions for the scroll test.
When entered, this value is placed into variable A:

1670 PRINT "Enter the Number of Repetitions-";A:PRINT

Line 1680 sets N to 31. N is the character string to be printed. The value 31 wi II
be the character string value with which the line is to begin:

1680 N =31

Line 1690 is the beginning of a FOR-TO loop which indicates the number of lines
to be printed as specified by the user in line 1670.

1690 FOR 1= 1 TO A

Line 1700 begins a series of instructions that serve to build and display a sliding
character string, 40 characters in length. N starts with character string 31, as
 Commodore Care Manual 73

indicated in line 1680. Line 1700 increments N until it gets to character string
71 (40 characters later). When N is incremented to greater than 71, N is brought
back to a value of 32:

1700 N=N+1:IF N>71 THEN N=32

Line 1710 is a FOR-TO loop which ensures that 40 characters are printed on each
line:

1710 FOR X=l TO 40

Line 1720 prints character string N, which will have a value between 32 and 71,
depending on where it is in the loop. N is incremented once each time it passes
through the loop:

1720 PRINT CHR$(N);:N=N+1

Line 1730 checks to see if N is greater than 71. If it is, N is set back to 32:

1730 IF N>71 THEN N=32

Lines 1740 and 1750 are the corresponding NEXT statements. The first one,
NEXT X, is for the 40 characters filling a single line. The second one, NEXT I,
is for the specified number of lines being printed to see the screen scrolling:

1740 NEXT X
1750 NEXT I

Line 1755 prints a blank line to prepare for the GOSUB instruction at line 1760:

1755 PRINT

Line 1757 checks the EX flag. If it is set to one, the program branches to line 1770:

1757 IF EX=1 THEN 1770

Line 1760 goes to the subroutine at line 3200, which prompts the user to press
any key to end the test:

1760 GOSUB 3200

Line 1765 branches the program back to line 800 to display the Monitor Diagnostic
Menu:

1765 GOTO 800

When the user presses 6 for the Sprite Test, the program branches to line
74 The Monitor

1770, which clears the screen and includes the identifying REMARK statement:

1770 GOSUB 2990 REM "Sprite Test"

Li ne 1 780 prepares the screen display for the Sprite Test by pri nti ng the test name:

1780 PRINT TAB(15)"Sprite Test"

Line 1790 is a FOR-TO loop which sets all the sprites' pointers to 13 in or-
der to activate them. Locations 2040 through 2047 are sprite firmware locations.

1790 FOR 8=2040 TO 2047:POKE S,13:NEXT

Line 1792 is a sprite definition, indicating that the sprite is to appear as a

white box, which is created with this FOR-TO instruction. POKE S.255 defines
the shape of the sprite as a square. The cassette buffer is used to temporarily hold
this sprite definition for the purpose of this test. Each of the eight sprites are de-
fined in this manner, one at a time:

1792 FOR 8=832 TO 894:POKE S,255:NEXT

Line 1800 sets V equal to 53248, which is another firmware location for the
sprite registers. Memory location V + 21 is POKEd to a value of 255. Th is informs
the system that all eight sprites will be used:

1800 V=53248 POKE V+21,255

Line 1810 is another FOR-TO loop, which colors the sprites white. This is
done with the instruction S = 39 TO 46. The values 39 through 46 dre the eight
locations of the eight sprites. V, which was set in line 1800, is POKEd into the
value of S, which is 29 through 46. The value 1 indicates that the sprites are to
be colored white:

1810 FOR S=39 TO 46:POKE V+S,1:NEXT S

The program then falls through to line 1820, which moves the eight sprites, one
at a time, across the screen with a FOR-TO loop:

1820 FOR I = 0 TO 7

Li ne 1830 uses d POKE and PEEK logic statement in order to activate the
individual sprites for individual testing. Because this is in a FOR-TO loop, it begins
with zero, and increments up through seven, to test all eight sprites:

1830 POKE 53269,PEEK(53269)OR(211)

 Commodore Care Manual 75

Line 1840 is another FOR-TO loop which sets up the XY coordinates to place
the location of the sprite. The sprite will move from left to right, which is
represented by the values 24 (at the left edge of the screen) through 255 (almost
to the right of the screen):

1840 FOR X=24 TO 255

Lines 1850 through 1890 consist of more POKE statements and FOR-TO
statements which cause the sprite to continue on to the right edge of the screen.
Line 1870 uses the array R, which was initialized in line 35:

1850 POKE (V+I*2),X:POKE (V+I*2+1),152

1860 NEXT X
1870 POKE (V + 16),R(I)
1880 FOR X=O TO 65
1890 POKE (V + (I * 2)),X: POKE (V + (I * 2 + 1)), 152z
1895 NEXT X

C128 USERS: Lines 1790 through 1880 of the e128 code are completely
modified to reflect the system's method of programming sprites. This
particularly involves the special sprite-related commands, SPRITE and
MOVSPR. Refer to Appendix B for the actual code.

Line 1897 resets the sprite X pointer back to the left edge of the screen:

1897 POKE V+16,PEEK(V+16)AND 254

Line 1900 turns off the sprite currently being tested so that the next sprite can
be tested in the same manner:

1900 POKE 53269,PEEK(53269)AN 0(255 - 2 I)

Line 1910 is a NEXT statement which lets the program move on to the next sprite
to be tested. This loop continues until all eight sprites are tested from left to right:

1910 NEXT I

Line 1915 checks for the EX flag. If it is set to one, the program returns to the
Exerciser module:

1915 IF EX=1 THEN RETURN

Line 1920 prints a blank line, and then branches to the subroutine which prompts
the user to press any key to end the Sprite Test:

1920 PRINT:G08UB 3200

Line 1930 returns the program back to the Monitor Diagnostic Menu:

1930 GOTO 800

 Chapter 4
Tile Printer
Although visual computer output is available from the monitor, this output is of-
ten needed in a physical hardcopy form as well. Printed output allows more
detai led scruti ny of the information; and allows presentation to others. The pri nt-
er is the means with which you can make a paper copy of computer processing
results.

DESCRIPTION AND FUNCTION OF THE PRINTER

The printer is like a typewriter without the keyboard. It is ordinarily an optional
device for your computer, because a printer is not necessary in order to run
programs and process data. To see results on paper instead of just on the monitor
screen, however, you must have a printer.

Types of PrInters
There are a myriad of printers available on the market today which work with
the Commodore. A printer is a standard peripheral, but you need to make sure
that the printer has a serial bus interface connector. Aside from that, Commodore
printer choices consist of the dot-matrix printer and the letter-quality printer.
The Dot-Matrix Printer. If a character on the monitor screen were magnified,
you would see that instead of being made up of solid lines, the character is in
fact composed of a series of light dots. Each character is typically composed of
seven or more dots. The series of dots used to build characters is called a dot matrix.

76
 Commodore Care Manual 77

The dot-matrix printer uses the same method as the monitor does for building
characters to print letters on paper. In the printer there is a single print head with
an array of small wires. When a character is sent to the printer, this print head
punches out the shape of the character through the ink ribbon to create its
impression on the paper (Fig. 4-1).
The dot-matrix printer provides output very quickly, and is the least expensive
printer available. Speed is measured in characters per second, or "cps." This speed
refers to how fast the printer can lay down characters on paper. A dot-matrix printer
can range in speed from 30 to 200 cps, possibly more.
The wide range of possible speeds is attributed to several factors. The most
obvious is how fast the computer can feed data to the printer.
Some printers print only left to right. These are called unidirectional printers.
Others can print both left to right and right to left. These are called bidirectional
printers, and they lay characters down on a page much faster, since no time is
wasted in sending the print head back to the "beginning" of a new line.
Some dot matrix printers offer several qualities of print. These different qualities
might include a draft, near-letter-quality, and letter-quality modes. The draft mode
might print a minimum number of dots for a character, thus taking the least amount
of time. The other modes use multiple print passes and more dots to make a darker,
more solid-looking character with better resolution. The tradeoff for higher quality
printing is speed.
In addition to the advantages of speed, the dot-matrix printer is attractive
because of its ability to produce an unlimited number of character font styles and
point sizes. Certain dot-matrix printers, called graphic printers, Can render graphic
characters. A graphic printer can address just as many ink points (which correspond
to the monitor's pixels) as your monitor resolution can display. This type of print-
er can reproduce graphic characters, as well as drawings and business graphics.
Any shape can be created with a series of dots. This makes the dot-matrix printer
highly flexible in terms of the output that can be created.
There are also dot-matrix printers that can print in different colors. The major
difference is that the printer uses a multicolored ribbon ..
The Letter-Quality Printer. Another very popular printer is the letter-quality
printer, sometimes referred to as a daisy-wheel printer. On such a printer, the
output looks as though it were typed on a typewriter.
The letter-qual ity printer is often preferred by people who use computers to

Fig. 4·1. Dot-matrix print head.

PRINT HEAD
78 The Printer

Fig. 4-2 . Daisy wheel.

do mass mailings as part of their business. Letters printed on a letter-quality print-

er look as though they were individually typed on a typewriter, not mass-produced
with a computer. In fact, any document that you want to look particularly
handsome is best done with a letter-quality printer. Letter-quality output simply
looks cleaner, with sharper characters than dot-matrix output.
The letter-quality printer uses a daisy wheel to create the characters. On the
end of each "petal" of the daisy wheel is a character (Fig. 4-2).
The daisy wheei includes the entire character set for a given font family and
point size. Instead of being formed by a single print head with a series of dots,
these characters are individually and solidly embossed into the daisy wheel. A
printer motor spins the daisy wheel around. When the desired character spins
into position, the print hammer strikes it against the ink ribbon to form the character
on the paper. It works on a principle similar to the typewriter, except that the
motor-driven printer is much faster.
Although the daisy wheel is the most common print element used in letter-
quality printers, character thimbles and cups are also used in some printers (Fig.
4-3). They work in the same general manner as the daisy wheel.

Fig. 4-3. Character cup.

 Commodore Care Manual 79

Printer Interfaces
The printer is physically connected, or interfaced to the computer through
a receptacle on the back of the system unit which accepts the printer's cable.
There are two major ways a printer can interface with a computer: parallel
and serial. The difference between these two interfaces is the manner in which
the data is transferred. A parallel interface pushes seven or eight bits of data in
one transfer. The serial interface sends data one bit at a time, in a series (Fig. 4-4).
Commodore systems only support serial printers. Parallel printers are not
compatible with these systems.

TROUBLESHOOTING AND REPAIR GUIDELINES

There are a number of problems the printer might experience, whether it is
a dot-matrix or letter-quality printer. The following sections describe these potential
problems, indicate how to diagnose them, and explain the steps necessary to re-
pair them.

Problem: The Printer Does Not Work

Suppose you've just bought a new printer, or you've moved your system.
Everything is in place, you issue a print command from the application software,
but nothing happens at all. There can be several problems associated with this.

[2] Solutions

o First check that power is applied to the printer. The printer has a power indicator
light on the top or front of the chassis. If the printer's ON/OFF switch is in
the ON position, but the indicator is not lit, make sure the printer is properly
plugged in. If it's plugged in but still not working, try using a different electrical
plug. Check whether this plug is controlled by a light switch.

o Make sure the printer is in the proper mode. Most printers have an ONLINE
mode which indicates that it is ready to receive data from the computer. They
might also have a LOCAL mode which allows you to physically manipulate
the printer: roll the paper, prepare the printer for a different form, or adjust

- r---

0
cr: cr: cr: cr:
w 0 w w w
I- 0 I- I- I-
:::> z :::> Z
0 c..
tL
~ 0
a:
c.. ~ cr:
c..
0 o
U u

'--- '---

Parallel Transfer of Data Serial Transfer of Data

Fig. 4-4. Parallel and serial data transfer.
80 The Printer

the platen. To get the printer operating again, switch it back to the ONLINE
mode.

iJ Check the cabling. Make sure you have the right kind of cable for the printer.
Make sure the cable is inserted into the proper plugs, and that it is sufficiently
secured and tightened down between the printer and the system interface port.

o Check that the application program is addressing the printer correctly. The
printer might not be working because the correct printer driver has not been
installed for this application.
The driver is activated by a printer installation program provided with your
application software. This special utility program lets you tell the program what
make of printer is being used so that the output to the printer is produced
correctly. It also ensures that any special printing functions such as boldface
and italic can be used.
The printer installation program provides numerous models from which
to choose. Even off-brand printers always have an equivalent to one of these
choices. If you do not run the application's printer installation program, the
driver might not be installed properly, and the printer would not work.

o Certain option switch settings within the printer might be making it impossible
to print. Such switch settings might control parameters such as "baud rate"
and "word length." Refer to the printer documentation for more information
about these switch settings. For more information about what the terms "baud
rate" and "word length" mean, refer to Chapter 7, "The Serial Communication
Interface. "

Problem: Poor Print Quaiity

One problem you might notice is that the print image quality is poor. While
the characters are recognizable, they look blurred, light, washed out. A related
problem can occur when printing on a multiple copy form. While the top copy
prints well, subsequent copies print poorly or not at all.

'vi SolutIons

LJ Run the Sliding Alpha or Display Print Character Test of the Printer Diagnostic
to obtain sample output. Poor print qual ity is usually a mechanical rather than
a software problem.

D Check the printer ribbon. It might be jammed or spent. When this happens,
the print heads strike the same place on the ribbon, and the ribbon is unable
to advance to fresh ink. Unjam the ribbon, or install a new ribbon cartridge.

[1 Some printers have a iorms adjustment. This adjustment causes the print head
to be brought further back from the platen to accommodate paper of heavier
thicknesses, or multipart forms. Use the forms adjustment to move the head
closer to the platen. Run a print sample again, and adjust the head until the
print image is clear and sharp again.
 Commodore Care Manual 81

o Clean the letter-quality daisy wheel or the dot-matrix print head with a lint-
free cloth or cotton swab moistened with isopropyl alcohol.

D If the print quality is still unacceptable after changing the ribbon, adjusting
the print head, and cleaning the element, refer to the printer documentation.
Call the manufacturer for more information.

Problem: A Horizontal Tab Is Not Working

If the printer seems to be unable to tab over to a certain position along the
carriage, run the Horizontal Tab Test. The asterisks should print in a diagonal
across the paper starting at position 1.

B Solutions

D If the tabs do not print in this diagonal, check whether something is obstructing
the platen (the cylinder around which the paper rolls) or the print head. Of-
ten, simply blowing through the print head or pulling out a bit of paper hung
on it will solve the problem.

D If this does not solve the problem, refer to the printer documentation, or contact
the manufacturer.

Problem: Paper Does Not Feed Properly

The printer might not feed the paper correctly. Certain commands issued from
the application program to the printer can cause the paper to feed several lines,
like carriage returns on a typewriter. When working with special forms like checks
and invoices, the application program helps you set up the line spacing to occur
in a specific pattern that is more complex than simple single- or double-spacing.
In addition, you might enter a form feed command at a certain defined point,
thus causing the printer to roll up to the next form.
Problems can occur when the specified vertical spacing does not work as
expected. You might not see the specified number of lines between text, or the
paper might bunch up and jam as it's rolling to the next page. These types of
problems usually occur upon initial printer setup.

B Solutions

D Run the Line Feed Test of the Printer Diagnostic Module to check the carriage
control. This test prints lines with variable line spacing and then feeds the pa-
per up to the next page.

D If the Line Feed Test does not take place as expected, check that the paper
has been fed into the printer correctly.

D If you are working with continuous-feed paper on a forms tractor, check that
the paper is not pulled too tight or left too loose in the tractor clamps.

LI Check the platen adjustment. There is a lever that unlocks the platen when
82 The Printer

rolling the paper in. In order for the paper to automatically feed with the forms
tractor, the platen must be set at the locked position.

D Check for a scrap of paper or other foreign object that might be lodged in
the platen or in the paper feed area.

D If you suspect that the printer is inserting extra spaces between lines, run the
Sliding Alpha Test of the Printer Diagnostic. The output should appear single-
spaced. If there are blank line spaces between the printed lines, faulty option
switch setting might be causing the extra line feeds. Check your printer
documentation for more information about the switch settings.

D If none of the above suggestions repair the line spacing problem, refer to your
printer documentation for the manufacturer recommendations.

Problem: CertaIn Characters Do Not PrInt

Sometimes a certain character does not print. The character exists on the
screen, and you know it's available within your printer's character set. However,
when you request printer output, the character does not form properly, or there
is a black box or blank space where the character should be. This means different
things, depending on whether you have a dot-matrix printer or a letter-quality
printer.

B SolutIons

D If you're working with a dot-matrix printer, run the Display Character Print
or Echo Character Test of the Printer Diagnostic. If you see that black box or
blank space where a character is supposed to be, then the printer is probably
not set up to accommodate graphics.
As discussed earlier, there are several types of dot-matrix printers. One
type accommodates graphic characters as well as the standard alphanumeric
characters. Another type operates only in the character mode. If yours is a
character printer, you cannot print graphic characters.
It might be confusing to see the graphic characters on your monitor display,
and yet not be able to print them. This is because different makes of printers
support different character sets. Some character sets are more limited than
others. Therefore, be sure to send only valid characters to the printer.
The Commodore provides two graphic character sets. You might be
attempting to print a character that is not in the currently active character set.
The character set printed is the one that is active when the printer is powered
on.
D In the case of a letter-quality printer, the daisy wheels are limited in size and
can usually only accommodate about 100 characters, upper- and lowercase.
Because of this, it is likely that the daisy wheel you're using does not include
any special graphic characters. (However, you can get special graphic daisy
wheels consisting of such special characters as part of their character sets.)

D If you're having trouble with regular alphanumeric characters, rather than

 Commodore Care Manual 83

Fig. 4-5. Broken character cup.

graphic ones, on your letter-quality printer, the problem is of an entirely

different nature.
For example, if the a's do not appear wherever they're supposed to, run
the Sliding Alpha or Echo Character Test of the Printer Diagnostic to see if
both the uppercase A and the lowercase a are missing. If this is the case, the
physical character position on your daisy wheel or cup has broken off its stem.
Daisy wheels and cups are fairly fragile, and characters can break after a period
of time (Fig. 4-5). Remove the daisy wheel and examine it to confirm that it
is indeed damaged. Buy a new daisy wheel to replace the broken one.

Problem: CertaIn Characters Do Not PrInt Completely

A potential dot-matrix printer problem is that while all the characters do print,
they do not print completely. In this case, it would not be just one or two individual
characters that have this problem, but the entire character set. Only part of the
a, part of the r, and part of the m, might be displayed, and the segment of the
character that's missing is in the same location of each character, such as the upper
left or lower right (Fig. 4-6).

B SolutIons

o First check the ribbon. It might be folded down or spent. Replace the ribbon
and run the Sliding Alpha or Display Character Print Test to print sample output.

o If the ribbon is in good condition, then there is a problem in the print head.
One of the solenoids that drives the dot matrix pins in the head has probably
malfunctioned or worn out, and that would explain the partially formed
characters. Take the printer in for servicing to have this solenoid motor repaired
or replaced.

• •••
• •••
Fig. 4-6. Incompletely printed
• •• • • •• •
characters.
••••••••• •••• ••
• • •••••• •• • ••• •
84 The Printer

Problem: Installing a New PrInter

The majority of printer problems occur upon initial installation. This is because
there are several variables that must be taken into account when installing a new
printer.
For example, suppose you have been outputting your software processing
results to a particular dot-matrix printer with no problem whatsoever. One day,
you decide to upgrade to a letter-quality printer. You take the old printer out and
plug the new printer into your computer, and think you're finished. Upon run-
ning an application and attempting to print the results, however, you discover
that either the printer does not print at all, or that there are unexpected results.
This happens because, as far as the computer system is concerned, the new printer
is a completely foreign device. It is not addressable. As such, the computer and
new printer do not know how to effectively communicate with one another.

l"d SolutIons
o Particular rules, or protocols, must be followed in order for the various system
components to communicate and send data back and forth. The protocol that
the old printer understood might be quite different from the protocol that your
new printer understands.
To help alleviate this problem, many application programs include a
program called a device driver that is established for a particular printer. A
device driver is a program that recognizes a special peripheral device such
as a letter-quality printer. Many applications, especially word processors, need
to know the exact printer model so that special functions such as underlining
and boldface can be handled correctly.
The device driver lets you specify which printer is being used, and thus
can let the program communicate correctly with the printer. Refer to the user
manual of the application software for more information on configuring the
device driver.
o When connecting a printer to the Commodore, ensure that any software
programs that use the printer are set up to the proper interface. This information
should be provided with your various user documentation; documentation
for the computer system, the printer, and the software are all vital for
configuration.

o You might encounter other problems when setting up a new printer. Again,
read the printer documentation thoroughly before installing. Other
documentation that might help includes Chapter 6, "Input/Output Guide,"
of the Commodore 64 Programmers Reference Guide. The user guide for any
software programs with which you're going to use the printer can also be a
good resource. Consult the printer manufacturer for further information.

RUNt"'NG THE PRINTER DIAGNOSTIC MODULE

To run the Printer Diagnostic Module, follow the instructions provided in
"Running the Diagnostic Program" in Chapter 1. Then press P or p to initiate
the Printer Diagnostic Module. The screen clears, and the Printer Diagnostic Menu
 Commodore Care Manual 85

Printer Diagnostic

1 ... Sliding Alpha Test

2 ... Display Character Print Test

3 ... Echo Character Print Test

4 ... Horizontal Tab Test

5 ... Line Feed Test

Press CLR/HOME to End Diagnostic

Fig. 4·7. The Printer Diagnostic Menu

is displayed as shown in Fig. 4-7. To activate one of the printer tests, press the
corresponding number, 1 through 5.

Sliding Alpha Test

The printer Sliding Alpha Test is similar to the sliding alpha routine used in
the Scroll Test of the Monitor Diagnostic Module. On the printer, this test serves
two functions: to fully exercise the printer, and to get a quick look at the full
alphanumeric display character set available for your printer.
When you press 1, you are prompted to enter the number of lines you wish
to run. Enter the desired number and press RETURN. The printer begins printing
a sliding alpha pattern. It types a line full of as many repetitions of the character
set as will fit on a line. It then feeds up another line, slides one character to the
left, and prints the same line of characters again. At the carriage limit, it again
feeds another line, slides another character to the left, and prints the line of
characters. The program continues to do this for the number of lines you specified
(Fig. 4-8).
If nothing happens when you try to run this test, or if the results do not look
similar to the illustration, refer to "Troubleshooting and Repair Guidelines" earlier
ill this chapter.

Display Character Print Test

The Display Character Print Test displays all characters available within the
86 The Printer

o
o ~"'S\&'(l"+,- '012J456789:;(:::)".ABCDEFGHIJF'LHNOPQRSTUVWXYZ( ]-_ abcdef9hijklmno
0
0
o ! "IS'\&' ( ) *+ -
"ltS\&'()· .. ,-.
10123456789:; (::: >., .... BCDEFGHIJKLMNOPQRSTUVWXYZ [\ J . _ 'abcdetqhi jklmno
012J456789:·(">?"BCDEFGHIJKLHNOPQRSTUVWXYZ[\] "_'abcdef ohijklmno! 0
o 0
o 0
o 0
o 0
o 0
o 0

QV
Fig. 4-8. Sliding Alpha Test results.

printer's character set, including graphic characters, and is used to check wheth-
er all characters are printing satisfactorily_
This test checks both character sets_ You must have a dot-matrix printer in
order to print the graphic characters_
To run the Display Character PrintTest, simply press 2_ All characters in the
character set are printed (Fig_ 4-9)_ After printing the character set, the Printer
Diagnostic Menu is displayed once again_

o o
o ./0-:2345673.:> ., :2 ..
J: ...,:
~ .::
"'
d.
L..
"
:1
f
r~
:J
0 o
o
" E
O PQP37'J'/:..J.--: I- I :::::';:;;;Al.=l..r.s1::lJ!I;':~"AI..!J~" 31:: • _ - _ I ~

o I _ ~ I r
8P:~S-'J,/~,,:v:+J
J 11--_,.
I _ -
·~'··.-i-13c..;:J
_
a 1_:;;: I r •
~

-,
~

-
rl

/" ~
~ K L [1 N
..,. , I I I

o
o o
o o
o o
o o
o o
QV
Fig. 4-9. Display Character Print Test results.
 Commodore Care Manual 87

Echo Character Print Test

The Echo Character Print Test lets you enter a character and have it
immediately printed, or echoed, on the printer. The entered character is echoed
across all 80 columns of the printer. This test lets you ensure that a certain character
is indeed printing, and lets you check its appearance. Make sure it's a complete
character, and that it's not broken nor faded. This test also lets you check wheth-
er all columns along the printer carriage are accepting characters.
To run the Echo Character Print Test, press 3. You are prompted to enter the
character to be echoed. Function keys and cursor keys are disabled for this test.
Only valid character and graphic keys can be echoed. The printer prints this
character at all positions along the carriage, columns 1 through 80 (Fig. 4-10).
When it's fi nished, you can press any other character to have that character echoed.
When you press the ESC key, the Printer Diagnostic Menu is displayed once again.

Horizontal Tab Test

The Horizontal Tab Test checks all combinations of tabbing across the print-
er carriage. To run the Horizontal Tab Test, press 4. The printer prints an asterisk
at column 1, feeds a line, tabs to column 2, prints an asterisk, feeds a line, tabs
to column 3, prints an asterisk, and so on all the way through to column 80. In
this way, every horizontal tab position is checked. The printed result is a diagonal
line of asterisks running from the upper left corner to the bottom right corner of
the paper (Fig. 4-11).
If you do not get such a result, there might be a problem with the printer
mechanism, or the printer might need a switch setting adjusted. Refer to
"Troubleshooting and Repair Guidelines" earlier in this chapter for further
information.

o o
o EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE 0
o 0
o 0
o 0
o 0
o 0
o 0
o 0

2V
Fig. 4-10. Echo Character Print Test results.
88 The Printer

0 •• 0
0 • 0
••
0 • 0
••
0 •• 0
0 •• 0
0 •• 0
0 •• 0
0 •• 0
••
0 • 0
0
0
""'- /
Fig. 4-11. HOrizontal Tab Test results.

LIne Feed Test

Line feed problems are manifested by text printing on top of previous lines
because the printer failed to feed a line where it was supposed to. The printer
might jam whenever it is supposed to feed a number of lines, or go to the next
page with a top-of-form command_
The Line Feed Test checks the printer's vertical line spacing, and is selected
by pressing 5 from the Printer Diagnostic Menu. Like the Horizontal Tab Test,
this test needs no additional paramf'tf'rs f'nterf'd, anri runs as soon as it is selected.
The printer types the first line. Then it gives two line feeds, types the second
line, gives three line feeds, types a third line, gives four line feeds, types a fourth
line, gives five line feeds, and types a fifth line. Finally a form feed command
is issued, and the printer rolls up to the next page and prints a line.
Line spacing and form feeding are often controlled by switch settings. If the
results are unsatisfactory, refer to "Troubleshooting and Repair Guidelines" in
the previous section for more information.

HOW THE PRINTER MODULE WORKS

Selecting P or p from the System Diagnostic Main Menu causes the program
to branch to line 3500, which is the beginning of the Printer Diagnostic Module
(Fig. 4-12).

3500 REM" Printer Diagnostic Module"

Line 3510 begins with a GOSUB instruction to line 2900 to clear the screen and
position the cursor:

3510 GOSUB 2900:PRINT TAB(11) "Printer Diagnostic":PRINT

3515 PRINT TAB(3)" 1 ... Sliding Alpha Test" PRINT
 Commodore Care Manual 89

3500 REM "Printer Diagnostic Module"

3510 GOSUB 2900:PRINT TAB(l1) "Printer Diagnostic":PRINT
3515 PRINT TAB(3)"1 ... Sliding Alpha Test":PRINT
3517 PRINT TAB(3)"2 ... Display Character Print Test":PRINT
3518 PRINT TAB(3)"3 ... Echo Character Print Test":PRINT
3519 PRINT TAB(3)"4 •.. Horizontal Tab Test":PRINT
3520 PRINT TAB(3)"5 ... Line Feed Test":PRINT
3530 PRINT TAB(5)"Press CLR/H()oIE to End Diagnostic
3535 OPEN l,4,7:REM "Open as Upper/Lower case"
3540 GOSUB 3000:IF ASC(A$)<>19 THEN 3560
3550 CLOSE 1:GOTO 50
3560 IF A$="1" THEN 3630
3570 IF A$="2" THEN 3750
3580 IF A$="3" THEN 3920
3590 IF A$="4" THEN 4010
3600 IF A$="5" THEN 4070
3610 GOSUB 3100:GOTO 3540
3630 REM "Sliding Alpha Test"
3640 GOSUB 2990:PRINT TAB(11) "Sl iding Alpha Test":PRINT
3645 INPUT "Enter the nL.mber of repetitions-";X
3650 N=31
3660 FOR 1=1 TO X
3670 L$="":N=N+1:IF N>111 THEN N=32
3680 FOR A=1 TO 80
3690 L$=L$+CHR$(N):N=N+1
3700 IF N>111 THEN N=32
3710 NEXT A
3720 PRINT#1,L$;:NEXT I
3730 IF EX=1 THEN GOTO 3760
3735 CLOSE 1
3740 GOTO 3500
3750 REM "Display Character Print Test"
3760 GOSUB 2990:PRINT TAB(6)"Display Character Print
Test":L$="":N=1
3770 CLOSE 1
3780 OPEN 1,4:REM "Open as Upper Case Only"
3790 FOR 1=32 TO 255
3800 IF N=80 THEN PRINT#1,L$;:N=1:L$="":GOTO 3820
3810 L$=L$+CHR$(I)+" ":N=N+1
3820 NEXT I
3830 CLOSE 1
3840 OPEN 1,4,7:REM "Open as Upper/Lower Case"
3850 FOR 1=32 TO 255
3860 IF N=80 THEN PRINT#1,L$;:N=1:L$="":GOTO 3880

Fig. 4-12. The Printer Diagnostic Module listing.

90 The Printer

3870 L$=L$+CHR$(1 )+" ":N=N+1

3880 NEXT I
3890 IF L$<>"" THEN PRINT#1,L$
3900 IF EX=1 THEN GOTO 3950
3905 CLOSE 1
3910 GOTO 3500
3915 REM "Echo Character Print Test"
3920 GOSUB 2990:PRINT TAB(7)IIEcho Character Print Test":
PRINT
3925 PRINT TAB(5)"Enter the Character to Echo":PRINT
3935 PRINT "Press the CLR/HCJoIE Key to End the Test"
3940 GOSUB 3000:IF ASC(A$)=19 THEN CLOSE 1:GOTO 3500
3950 L$=""
3970 FOR 1=1 TO 80
3980 L$=L$+A$:NEXT
3990 PR I NT#1 , L$
4000 GOTO 3940
4010 REM "Horizontal Tab Test"
4020 GOSUB 2990:PRINT TAB(10)"Horizontal Tab Test"
4030 FOR 1=1 TO 80
4040 PRINT #1,TAB(I)"*":NEXT
4050 IF EX=1 THEN GOTO 4080
4060 CLOSE 1:GOTO 3500
4070 REM "Line Feed Test"
4080 GOSUB 299O:PRINT TAB(13)"Line Feed Test"
4100 FOR 1=2 TO 10
41'0 FOR A=1 TO I
4115 PRINT#1,'"':NEXT A
4120 N$=STR$(I-1>
4130 PR 1NT#1, "There have been "; N$;" line feeds"; :NEXT I
4140 IF EX=1 THEN RETURN
4150 CLOSE 1:GOTO 3500

Fig. 412. The Printer Diagnostic Module listing. (Continued from page 89.)

3517 PRINT TAB(3)"2 ... Display Character Print Test":PRINT

3518 PRINT TAB(3)"3 ... Echo Character Print Test":PRINT
3519 PRINT TAB(3)"4 .. Horizontal Tab Test":PRINT
3520 PRINT TAB(3)"5. . Line Feed Test":PRINT
3530 PRINT TAB(5)" Press CLR/HOME to End Diagnostic

The balance of line 3510, together with lines 3515 through 3530, displays the
Printer Diagnostic Menu.
Line 3535 opens the printer in the upper/lowercase character set mode:

3535 OPEN 1,4,7 REM "Open as Upper/Lower case"

 Commodore Care Manual 91

Line 3540 accesses the keyboard input subroutine, and waits for the user to press
a key indicating the printer test choice:

3540 GOSUB 3000:IF ASC(A$)< >19 THEN 3560

If the user presses the CLRlHOME key (character string value 19), the program goes
to line 3550, which closes the printer and returns to the System Diagnostic Main
Menu:
3550 CLOSE 1:GOTO 50

When the user presses a key other than CLRlHOME, the program branches to
lines 3560 through 3600:

3560 IF A$="1" THEN 3630

3570 IF A$= "2" THEN 3750
3580 IF A$= "3" THEN 3920
3590 IFA$="4"THEN4010
3600 IF A$= "5" THEN 4070

These particular instructions check whether values 1, 2, 3, 4, or 5 reside in variable

A$. For example, if the user presses 1, the program branches to line 3630, the
beginning of the Sliding Alpha Test.
If the user presses something other than 1 through 5, the program falls through
to line 3610, sounding the beep which alerts the user that an invalid function
has been entered:

3610 GOSUB 31 OO:GOTO 3540

The program returns to line 3540, at which point the user can try again with a
valid key.
When the user presses 1, the program branches to line 3630 for the SI iding
Alpha Test:

3630 REM "Sliding Alpha Test"

Line 3640 clears the screen and displays the Sliding Alpha Test title. The INPUT
statement at line 3645 prompts for the number of repetitions to be printed. This
number is placed into variable X:

3640 GOSUB 2990:PRINT TAB(11) "Sliding Alpha Test":PRINT

3645 INPUT " Enter the number of repetitions- ";X

Variable N holds the value of the characters to be included in the line which
successively builds the sliding alpha pattern. In line 3650, N is set to 31. This
is one less than 32, the character string value for a blank space:

3650 N =31
92 The Printer

Line 3660 is the beginning of a FOR-NEXT loop:

3660 FOR I = 1 TO X

This determines the number of lines to be printed, so it is FOR one to X; X being

the number of repetitions specified at line 3645.
Within this FOR-NEXT loop, L$ is set to null, and a one is added to N:

3670 L$="":N=N+1:IF N>111 THEN N=32

N starts out as 31, and then becomes 32, the character code for the blank space
character. If N is greater than 111, N is reset back to 32. The characters with values
between 32 and 111 are printed. Once 112 is reached, the IF statement causes
N to return to 32. This prevents invalid characters, such as ESC sequences, from
being printed. It also causes the string to slide by one character for each line that
is printed.

Another FOR-NEXT loop begins at Line 3680:

3680 FOR A= 1 TO 80
3690 L$= L$+CHR$(N):N = N + 1

This builds the actual line to be printed. A character determined by N is added

to L$. This character starts out again as CHR$ value 32, the blank space character.
Then one is added to N to get the val ue for the next character.
Line 3700 begins a test similar to the test done in line 3670:

3700 IFN>111THENi'-J=32
3710 NEXT A

Again, if N is greater than 111, N is reset to CHR$ value 32, the blank space
character. The statement NEXT A causes the characters to fill an entire line.
Once all the characters have built an 80-character line, which is the printer
carriage width, the program proceeds to line 3720:

3720 PRINT#1 ,L$;:NEXT I

This causes the output of L$ to go to the printer instead of to the monitor. The
semicolon prevents a line feed. The NEXT I means that one of the repetitions
has been carried out. This routine prints the lines for the specified number of
repetitions.
When the number of repetitions entered into the INPUT statement for X is
satisfied, the program goes to line 3730, which checks whether variable EX is
equal to one. If it is, then the Exerciser Module is in control, and the program
branches to line 3760. If EX is equal to zero, then the program proceeds to lines
3735 and 3740. The printer is closed, and the program branches back to display
the Printer Diagnostic Menu:
 Commodore Care Manual 93

3730 IF EX= 1 THEN GOTO 3760

3735 CLOSE 1
3740 GOTO 3500

When 2 is pressed, the program goes to the Display Character Print Test start-
ing at line 3750:

3750 REM Display Character Print Test

3760 GOSUB 2990:PRINT TAB(6)" Display Character Print
Test" :L$ = " " :N = 1

Line 3760 clears the screen and then displays the test title. As before, L$ is used
to build the print line, and is set to null. N is set to one.
Line 3770 closes the printer so it can be opened to print in the uppercase
graphics character mode:

3770 CLOSE 1

Line 3780 reopens the printer in this mode:

3780 OPEN 1,4:REM "Open as Uppercase Only"

Lines 3790 through 3820 form a FOR-NEXT loop which prints the complete
uppercase graphic character set:

3790 FOR 1=32 TO 255

3800 IF N=80 THEN PRINT#1,L$;N=1:L$="":GOTO 3820
3810 L$=L$+CHR$(I)+" "N=N+1
3820 NEXT I

Lines 3830 and 3840 close and reopen the printer in the upper/lowercase mode:

3830 CLOSE 1
3840 OPEN 1,4,7:REM "Open as Upper/Lowercase"

Line 3850 prints the upper/lowercase graphic character set, cycling through values
32 to 255. These are the values for the standard CHR$ display codes (blank space,
A through Z, 1 through 0, etc.).

3850 FOR 1=32 TO 255

Line 3860 checks to see if variable N is equal to the carriage width of 80 characters:

3860 IF N=80 THEN PRINT#1,L$;:N=1:L$="":GOTO 3880

If N =80, a full line has been built, and L$ is output to the printer, device #1.
94 The Printer

In this case, the line feed is not suppressed as in the previous test, so the test
is double-spaced. N is reset to one and the program skips to line 3880, the NEXT
I statement.
If N is not equal to 80 at line 3860, the program falls through to 3870, which
concatenates the next character onto the L$ and adds one to N:

3870 L$=L$+CHR$(I)+" ":N=N+1

This loop continues until a" character positions have been printed:

3880 NEXT I

Because a full line is not builtforthe part of the character set, L$ must be dumped
after the FOR-NEXT loop. Line 3890 accomplishes this:

3890 IF L$<>"" THEN PRINT#1,L$

Line 3900 checks whether the EX flag is set to one. If it is, the Exerciser Module
is operating, and the program branches to line 3950:

3900 IF EX = 1 THEN GOTO 3950

Line 3905 closes the printer:

3905 CLOSE 1

Line 3910 returns the program to display the Printer Diagnostic Menu:

3910 GOTO 3500

When the user enters 3 from the Printer Diagnostic Menu, the program
branches to line 3915 for the Echo Character Print Test:

3915 REM "Echo Character Print Test"

At 3920, the screen is cleared, and the test name is printed:

3920 GOSUB 2990:PRINT TAB(7)"Echo Character Print Test":

PRINT

Line 3925 prompts the user to enter the character to be echoed on the printer:

3925 PRINT TAB(5)" Enter the Character to Echo":PRINT

Line 3935 prompts the user to press the ESC key to end the test:

3935 PRINT " Press the CLR/HOME Key to End the Test"
 Commodore Care Manual 95

Line 3940 goes to the Get-a-Key subroutine at line 3000. As before, if the
value of A$ is equal to character string value 19 (the CLRlHOME key), the program
closes the printer and then branches back to the Printer Diagnostic Menu:

3940 GOSUB 3000:IF ASqA$) = 19 THEN CLOSE 1:GOTO 3500

Line 3950 sets L$ to a null value:

3950 L$=""

Once the user enters a valid key to be echoed, the program falls to 3970,
which is a FOR-NEXT loop:

3970 FOR 1=1 TO 80

As before, 80, the carriage length, is used as the parameter for how far the character
is to be printed.
Line 3980 takes the entered character and joins it with L$ for the length of
the carriage:

3980 L$=L$+A$:NEXT I

Once all positions in the carriage width are filled, the program proceeds to line
3990.
Line 3990 outputs the contents of L$ to the printer:

3990 PRINT#1,L$

Line 4000 returns the program to line 3940, at which point the user can either
enter another character to be echoed, or press CLRlHOME to end this test and re-
turn to the Printer Diagnostic Menu:

4000 GOTO 3940

Pressing 4 from the Printer Diagnostic Menu branches the program to the
Horizontal Tab Test starting at line 4010:

4010 REM Horizontal Tab Test

4020 GOSUB 2990:PRINT TAB(10)"Horizontal Tab Test"

The screen is cleared and the test title is displayed.

Line 4030 begins another FOR-NEXT loop for the length of 80, the printer
carriage length:

4030 FOR 1=1 TO 80

96 The Printer

Line 4040 prints a series of asterisks using the TAB statement. This causes
horizontal tabbing:

4040 PRINT #1,TAB(I)"*":NEXT I

The TAB statement uses variable I of the FOR-NEXT loop as the tab value. It prints
an asterisk, then loops back to repeat for the next value of variable I. This causes
the asterisks to be printed in a stairstepped row.
After printing this diagonal row of asterisks, the program proceeds to line 4050,
which checks whether variable EX is equal to one. If EX is equal to one, the
Exerciser Module continues at line 4080. If EX is not equal to one, the program
falls through to line 4060, which closes the printer and returns the program to
display the Printer Diagnostic Menu:

4050 IF EX = 1 THEN GOTO 4080

4060 CLOSE 1:GOTO 3500

The final test is activated by pressing 5. The program branches to line 4070
for the Line Feed Test:

4070 REM "Line Feed Test"

4080 GOSUB 2990:PRINT TAB(13)"Line Feed Test"

The screen is cleared, and the test title is displayed.

Line 4100 begins one of two FOR-NEXT loops:

4100 FOR 1=2 TO 10

This causes vertical line spacing with lines 2 through 10.

Line 4110 begins the second FOR-NEXT loop that has the printer producing
blank lines with simple carriage returns:

4110 FOR A = 1 TO I

This causes the printing to space the desired number of lines. On the first iteration,
2 is printed, followed by two line feeds.
Line 4115 prints the contents of the line to the printer, then goes on to the
next cycle of the FOR-NEXT loop:

4115 PRINT#l,"":NEXT A

The program falls through to line 4120, which sets N$ equal to the string value
of I. The (1-1) part of the statement makes sure that the first I ine feed actually takes
place on the first line:

4120 N$=STR$(I-1)
 Commodore Care Manual 97

This creates orderly output for line 4130, which is the message indicating the
number of lines that have been tabbed:

4130 PRINT#1,"There have been ";N$;" line feeds";:NEXT I

It then goes to the NEXT statement. This sequence repeats four more times.
After this is completed, line 4140 checks to see if EX is equal to one. If it
is not, the program proceeds to Line 4150:

4140 IF EX=1 THEN RETURN

4150 CLOSE 1:GOTO 3500

This causes the program to close the printer and then branch back to line 3500,
returning the program to display the Printer Diagnostic Menu.
 Chapter 5
Tile Casselle
Drive
The previous chapters have primarily covered computer input and output, the
keyboard being the major input device, and the monitor and printer being output
devices. However, when you wish to do anything even slightly sophisticated with
your computer, in addition to the facilities of input and output, you need one
more function: mass storage.
The system unit of the Commodore 64 can store 64 kilobytes (abbreviated
64K) of information at one time. The Commodore 128 system unit memory can
store 128 kilobytes of information at one time. This is fine until you want to turn
the computer off. The Commodore systems have what is called a volatile memo-
ry. This means that in order for the memory chips to retain their information, power
must be continuously applied to their circuitry. Once the computer is powered
off, everything that was stored in that 64 or 128K is erased.
To prevent the loss of valuable programs and data, mass storage devices such
as the cassette tape drive and the floppy diskette drive are used. When you
command the computer to save a file, the program currently in system memory
is written onto the magnetic media, whether it is a cassette tape or a diskette.
The file is written in digital form, as a series of ON and OFF bits.
Likewise, when you command the computer to restore a saved file, the system
retrieves the information stored on the media (tape or diskette). It places it into
system memory just as it was last saved. This facility also allows you to buy
prerecorded programs and load them into your system.
While Chapter 6 covers the disk drive, this chapter deals solely with the
cassette drive.

98
 Commodore Care Manual 99

DESCRIPTION AND FUNCTION OF THE CASSETTE DRIVE

The cassette tape drive used with the Commodore is very similar to the cassette
machine in your home stereo or in your car. It has the same mechanics, and works
on the same principles. It loads the same size and type of cassette tape. It has
record/playback head(s), and several controls: RECORD, PLAY, FAST FORWARD,
REWIND, STOP, and EJECT. It might also have a tape counter, which is particularly
useful when storing several files on one tape.
The difference between the computer cassette drive and your stereo's cassette
player is that instead of recording and playing back music through a speaker, the
cassette drive records and "plays back" digital information through a computer.
This difference indicates the two storage functions the cassette drive provides:
recording, or writing information from the computer onto the tape; and playing
back, or reading information from the tape to the computer.

How the Cassette Drive Functions

The computer and the cassette drive operate in two entirely different
languages. The computer understands digital information consisting of ones and
zeros, or ON and OFF. The cassette drive, on the other hand, understands analog
information consisting of waveforms, or signal noise.
Fortunately, the two devices can translate their respective languages to
accommodate one another. This is accomplished with the cassette drive interface
cable. When the cassette drive cable is plugged into the appropriate connector
on the back of the Commodore, the translator is set up (Fig. 5-1).
Then, when there is data or a program you would like to save to tape, you
can type the appropriate command and press the RECORD button on the cassette
drive. The computer's digital information goes through the cassette interface and
is converted into an analog noise signal (Fig. 5-2). This "sound" is then input
to the cassette drive and recorded directly onto the tape media.
When there is previously stored data or a prerecorded program you would
like to retrieve, it works in the reverse. Load the cassette holding that information,
give the appropriate retrieve command from the computer, and press the PLAY
button on the cassette drive. The analog signal on the cassette tape moves from
the cassette drive and through the cassette interface. This time, the analog signal
is converted into a corresponding digital signal. This signal is then input to the
computer and the information is placed into system memory. You can now access
the information for display on the monitor and further processing as desired.

11000110110 Cassette Tape Drive

001111000111----..-j Interface Head
10001110000

CPU converts digital data to

memory analog signals magnetic tape
Fig. 5·1. The cassette tape drive Interface.
100 The Cassette Drive

Cassette
IlL..---system_unitJ~I
1101100 1100011 1111001

Fig. 5-2. Digital to analog signal conversion.

The Cassette Tape Media

The material in the cassette which stores this information is a magnetic media.
It is a type of plastic, called "mylar," that has been coated with iron oxide. Iron
oxide is a particular material that can hold a magnetic charge. When recording,
the record head of the cassette drive mechanism causes a specific magnetic pattern
in the form of an analog signal to be recorded onto this tape media (Fig. 5-3).
The tape media is wound from one spool to a second spool, and this is all
encased within a cassette. As the spools are turned with the PLAY, FAST FORWARD,
or REWIND controls on the cassette drive, the tape is fed from one spool to the
other in the indicated direction. This facilitates a linear, or sequential, access to
the recorded data (as opposed to a random access, which is the case with a disk
drive).
Various lengths of cassette tapes are available: 30-minute, 60-minute,
90-minute, and 120-minute. When choosing the length, consider whether you'll
be using a new tape for each new program or set of information, in which case
you might choose one of the tapes that are shorter in length. Also consider that
the 120-minute tape is made of a thinner mylar, and as such, it might be more
fragile than the others, and therefore might not be as reliable.
There are also varying degrees of cassette tape quality available from many
different manufacturers. Choose the quality in accordance with how you intend
to use the tape. For example, in the case of recording audio, lower-quality tapes
might be acceptable for recording a conversation or a meeting, but a higher-quality
tape is more desirable for recording high-fidelity music. Likewise, use low-quality

ANALOG REPRESENTATION OF DIGITAL DATA

ON CASSETTE TAPE

TRACK A

TRACK B

Fig. 5-3. Analog signals recorded on cassette tape.

 Commodore Care Manual 101

tapes to store the less important data, and high-quality tapes to store important
data and programs. And remember to make backups of everything.

NOTE: Whenever you write a program or data to tape, always make one
or two backups, just in case something goes wrong.

The Cassette Tape Drive

Your cassette drive might be the Commodore VIC Datasette, or it might be
a standard cassette tape machine. The Commodore Datasette cassette drive is made
for the specific purpose of reading and writing data. Because of this, the Datasette
has no volume control, tone control, or speaker. This simplifies the unit, because
there is no need for a speaker. The computer is not interested in audible sound,
but only the signal. Volume and tone settings are necessary, but the VIC Datasette
sets these functions internally, to prevent faulty read or write operations.
Nonetheless, any cassette tape machine can work successfully as the
Commodore's cassette drive, as long as it includes the RECORD and PLAY functions.
Be careful to set the volume and tone close to the higher settings, however. Ensure
that the settings are the same when you record material and when you play it
back. If the settings are changed, the data might not read back correctly.
Whichever type of cassette drive you use, it will include the RECORD, PLAY,
FAST FORWARD, REWI ND, STOP, and EJECT functions (Fig. 5-4). It will also have the
head mechanism, which is the device that magnetically records the data onto
the tape or reads the recorded information from tape. Finally, the cassette drive
will include the motor, which rotates the cassette reels to advance the tape.

Fig. 5-4 . Commodore VIC Datasette.

102 The Cassette Drive

TROUBLESHOOTING AND REPAIR GUIDELINES

There are several problems possible with the cassette drive. The following
sections identify these problems, indicate how to diagnose them, and describe
specific repair procedures.

Problem: The Cassette Drive Does Not Work

If nothing happens when you turn the cassette drive power on, insert a tape,
and press one of the buttons, there is a problem with the cassette, with power,
or with the system unit.

B Solutions

D First check the cassette tape itself. If you pressed PLAY or FAST FORWARD and
nothing happened, it could mean that the tape is wound all the way through.
Press REWIND. If it begins rewinding, then this certainly was the case. If it does
not rewind, and if the red LED does not light, a power problem is indicated.

D Check the power source. The VIC Datasette power is derived from the
Commodore system unit itself. Whenever the Commodore system unit is
powered on, the tape drive should power on along with it. The LED on the
front of the Commodore indicates that the system unit has power. If the LED
does not light up, check the power receptacle to which the Commodore is
connected. Check to see whether that receptacle is working, and whether it
is controlled by a switch.
A standard cassette tape drive is plugged directly into its own power
receptacle. In this case, check the power receptacle to which the cassette drive
is connected.

D If the Commodore system is on and functioning, and the power receptacle

is working fine, then check the cabling. As noted, the VIC Datasette drive cable
is a combination power cable and interface cable. A standard cassette drive
has its own power cable connected into the AC wall socket, and a separate
interface cable. In both cases, the interface cable runs from the back edge of
the cassette drive into an edge connector on the back of the Commodore system
unit (Fig. 5-5). Check that the cable is properly attached to the edge connector.

Fig. 5-5. Cassette drive interface connection.

 Commodore Care Manual 103

C If the cable looks secure on both ends, note that the cassette drive must be
connected to the system unit prior to powering on the system. If you tried
to connect the drive while the system unit is powered on, the system might
not have recognized that the drive was there. To check this, turn the system
off, turn it on, and try to load the tape again.

C If the tape still does not load, try swapping a different tape drive on your system.
If the swapped tape drive works on your system, there is a problem with your
cassette drive, and it should be replaced (it probably would cost as much to
repair a defective tape drive as it would to buy a new one).

o If the swapped tape drive does not work on your system, try using your tape
drive on a different system. If your tape drive works on a different system,
there is a problem with your system unit. Refer to the "Troubleshooting and
Repair Guidelines" in Chapter 2, and follow the instructions for troubleshooting
the system unit.

Problem: Drive Is not Reading or Writing Correctly

When attempting to read data, if the LOAD message remains on the screen
for an unusually long time, perhaps five minutes, for example, this indicates that
the system could not complete the load process. If the LOAD message is normal,
but garbled results or no results are displayed when you try to run the program,
there is either a problem with the cassette tape, with the cassette drive, or with
the system unit.
To test whether there is a write problem, you could write a program to tape,
then rewind it and give the VERIFY command. VERIFY is a Commodore function
which reads the tape and checks whether the material on the tape matches the
material currently in system memory. If this test fails, there is a write problem,
which again could originate from the cassette tape, cassette drive, or system unit.
The majority of the remedies for both read and write problems are the same, and
are as follows.

B Solutions

Ll First run the Cassette Tape Diagnostic, particularly the Read/\Nrite Test de-
scribed in the next section, "Running the Cassette Drive Diagnostic." Use
a new, blank cassette tape.
If the cassette drive passes the test, this indicates that the tape you tried
to read to or write from is defective. Use its backup. If the test fails, there might
be a problem in the read/write circuitry of the system unit. There are other
tests you should try, however, before delving into the computer itself.

o Load a cassette that you know is good-one that contains a program loaded
many times in the past without fail. If it does not load at first, try it again several
more times. Sometimes the tape will eventually read, but this is often an
indication of a problem with the cassette tape media. Immediately make a
backup, if you don't have one already.
104 The Cassette Drive

o If the test still fails, try loading yet another tape that has recently been
successfully loaded. If this tape loads, this means the other tape was defective.
Discard it and use its backup.

o If the second tape does not load either, try loading the tape on another system.
If the tape sti II does not load, the tape is defective. If it does load on the other
system, create a backup copy of the tape and try it again on your system.
If the backup works on your system, the tape was defective. However,
if the backup still does not work on your system, there might be a more ser-
ious problem with the cassette drive or the system unit.
o If you are using a standard cassette drive rather than the Commodore VIC
Datasette, check the levels of the volume and tone controls. If either of these
is set too low, the data signal will not be interpreted properly, causing an
unsuccessful read or write.
A good rule of thumb is to maintain both volume and tone controls at
least three-quarters of the way up. The ReadIWrite Test of the
Cassette Diagnostic Module can also help you determine the best levels.

o If you're not having trouble reading from a cassette tape, but are having trouble
writing, check the cassette tape itself-it might be write-protected . Cassette
tapes usually have a write-protect tab at the top, and if it has been broken
off, nothing can be saved on this tape.
You can easily make the tape write-enabled again by placing a small
piece of cellophane tape over the write-protect gap (Fig. 5-6) .

Write-protect tab
Write-p(otect tab for side B
for side A

Fig. 5·6. Write-enabling a write-protected cassette tape.

 Commodore Care Manual 105

D If the system is attempting to read and write information, but the results are
not accurate, the problem might be that the read/write head in the cassette
drive needs cleaning.
The cassette's mylar tape is coated with iron oxide that comes into direct
contact with the cassette drive's read/write head. This head magnetizes the
tape when writing (recording), or reads the magnetic pattern in the tape when
reading (playing).
Because of this direct contact, the iron oxide coating can rub off on the
head. Over a period of time, this residue on the head can begin to inhibit
its functions of reading and writing data.
To clean the iron oxide residue from the cassette drive head, moisten a
cotton swab or lint-free cloth with isopropyl alcohol. Rub the swab or cloth
over the head (Fig. 5-7). Now attempt to load the tape again.

D If there is still trouble reading or writing, try cleaning the cassette drive interface
edge connector. This edge connector can oxidize, and the oxidation can
prevent the necessary electrical connection.
To clean off the oxidation, use the pink eraser from the end of a pencil,
and rub it over the edge connector (refer to Fig. 2-6 for a photograph of this
procedure). Black or gray residue will be removed by the eraser.
Reconnect the cable and attempt to read or write the problem cassette
tape again.

D If problems persist, swap a different cassette drive on your system and load
a tape. If you are able to read/write a tape on the swapped tape drive, there
is a problem with your original cassette drive, and it should be replaced.

D If the swapped tape drive does not work on your system, swap your cassette
drive on a different system and load a tape. If you are able to read/write a
tape on the different system, a problem with your system unit is indicated.
Refer to the "Troubleshooting and Repair Guidelines" in Chapter 2, "The
System Unit/Keyboard," and follow further instructions for troubleshooting
the system unit.

Fig. 5-7. Cleaning the tape head.

106 The Cassette Drive

RUNNING THE CASSETTE DRIVE DIAGNOSTIC MODULE

To run the Cassette Drive Diagnostic Module, follow the instructions provided
in "Running the Diagnostic Program" in Chapter 1. Then press C to initiate the
Cassette Drive Diagnostic Module. The Cassette Drive Diagnostic Menu is
displayed (Fig. 5-8).
The Cassette Drive Diagnostic Module consists of two tests: the Write/Read
Test and the Read-Only Test. Use a blank cassette tape to run this test. The test
results might prove more accurate when using a new tape for testing. If you don't
have a blank cassette, at least use one containing data that is no longer needed.
This test will overwrite any existing data on the tape.
The Write/Read Test writes two files of 100 records each on the tape. It then
reads what it wrote, to ensure a match and therefore verify the integrity of both
the write and read circuitry. You should run this test and keep the tape as a test
tape for future use.
The Read-Only Test reads the two files of 100 records created in the
Write/Read Test. This is particularly useful when you suspect that the system is
experiencing problems with the read circuitry. Run this test on the test tape made
previously with the Write/Read Test to verify whether or not there is a problem.
To select the Write/Read Test, choose 1 from the Cassette Drive Diagnostic
Menu. You are prompted to insert a blank cassette tape into the cassette drive.
Make sure this tape is fully rewound to the beginning. Then, as prompted, select
the RECORD button, and press any key to continue.
The Write/Read Test then writes two files out to the tape. The first one has

Cassette Diagnostic

1 ... Write/Read Test

2 ... Read Only Test

Enter Command

Fig. 5-8. The Cassette Drive Diagnostic Menu.

 Commodore Care Manual 107

an alternating pattern of 10101010. The second one has the opposite pattern of
01010101. The program writes 100 records of these patterns to the tape.
Once this is done, you are prompted to press the cassette drive STOP button,
rewind the tape to the beginning, press the PLAY button, and press any key to
continue. The program reads both files containing the 100 records of alternating
bit patterns. As it reads, it compares each record to the value that was written.
If there is a discrepancy, an error message is displayed, indicating the number
of errors encountered during the test.
To select the Read-Only Test, enter 2 from the Cassette Drive Diagnostic
Menu. You are prompted to load the cassette tape to be read into the cassette
drive. Be sure to have the tape rewound to the beginning. Press PI AY, and then
press any key to continue.

HOW THE CASSETTE DRIVE MODULE WORKS

When the user presses C or c from the System Diagnostic Main Menu, the
program branches to line 4200. A REMARK statement at line 4200 indicates the
beginning of the Cassette Drive Diagnostic Module (Fig. 5-9):

4200 REM "Cassette Diagnostic Module"

Lines 4210 through 4250 clear the screen and display the Cassette I Jrive
Diagnostic Menu:

4210 GOSUB 2900

4220 PRINT TAB(10) "Cassette Diagnostic":PRINT
4230 PRINT TAB(10) "1 ... Write/Read Test":PRINT
4240 PRINT TAB(10) "2 ... Read Only Test":PRINT
4250 PRINT TAB(10) "Enter Command"

Line 4260 sends the program to the Get-a-Key subroutine at line 3000. A valid
character here is either 1 or 2, corresponding to the two tests within this diagnostic:

4260 GOSU B 3000

Lines 4270 and 4280 check for these values and branch to the appropriate places
in the code:

4270 IFA$~"1"THEN4310
4280 IF A$= "2" THEN 4420

If a key other than 1 or 2 was pressed, the program falls through to line 4290,
which sends for the Beep subroutine at line 3100. The program then proceeds
on to line 4300, which returns the program back to line 4260, letting the user
enter another key:
108 The Cassette Drive

4200 REM "Cassette Diagnostic Module"

4210 GOSUB 2900
4220 PRINT TAB(10) "Cassette Diagnostic":PRINT
4230 PRINT TAB(10) "1 ••. lIrite/Read Test":PRINT
4240 PRINT TAB(10) "2 ... Read Only Test":PRINT
4250 PRINT TAB(10) "Enter Coomand"
4260 GOSUB 3000
4270 IF A$="1" THEN 4310
4280 IF A$="2" THEN 4420
4290 GOSUB 3100
4300 GOTO 4260
4310 GOSUB 299O:PRINT TAB(13)"lIrite/Read Test":PRINT
4320 PRINT "Place a blank tape in the cassette drive"
4330 PRINT "and press RECORD.":PRINT
4340 GOSUB 3300:GOSUB 3000:PRINT
4350 OPEN 1,1,1, "Test-Tape 1"
4360 FOR 1=1 TO 100
4370 PRINT#1,CHR$(170):NEXT
4380 CLOSE 1:0PEN 1,1, 1 ,"Test-Tape 2"
4390 FOR 1=1 TO 100
4400 PRINT#l CHR$(85):NEXT
4405 CLOSE 1
4410 PRINT:PRINT "Rewind the tape and press PLAY"
PRINT:GOSUB 3200
4415 GOTO 4460
4420 GOSUB 2990
4430 PRINT TAB(13) "Read Only Test":PRINT
4440 PRINT "Place the test tape in the cassette drive"
4450 PRINT "and press PLAY"
4455 PRINT:GOSUB 3300:GOSUB 3000:PRINT
4460 OPEN l,1,O,"Test-Tape 1"
4470 FOR 1=1 TO 100
4480 INPUT#1,A$
4490 IF A$<>CHR$(170) THEN E=E+1
4495 NEXT
4500 CLOSE 1
4510 OPEN 1,1,O,"Test-Tape 2"
4520 FOR 1=1 TO 100
4530 INPUT#1,A$
4540 IF A$<>CHR$(85) THEN E1=E1+1
4550 NEXT I
4560 CLOSE l:PRINT
4570 PRINT TAB(3) "There were ";E;" High Value errors"
:PRINT

Fig. 5-9. The Cassette Drive DiagnostiC Module listing.

 Commodore Care Manual 109

4580 PRINT TAB(3) "There were ";E1;" Lo\ol Value errors"

:PRINT
4590 GOSUB 3200
4600 GOTO 50

Fig. 5·9. The Cassette Drive Diagnostic Module listing. (Continued from page 108.)

4290 GOSUB 3100

4300 GOTO 4260

When the user presses 1, the program branches to line 4310 for the Write/Read
Test. Here, the screen is cleared with the Clear Screen subroutine, and the title
is displayed at the top of the screen:

4310 GOSUB 2990:PRINT TAB(13)"Write/Read Test":PRINT

Lines 4320 through 4340 display the necessary user prompts:

4320 PRINT "Place a blank tape in the cassette drive"

4330 PRINT "and press RECORD.":PRINT
4340 GOSUB 3300:GOSUB 3000:PRINT

The program then falls through to line 4350, which opens the tape device
and assigns the name of "Test-Tape 1" to the first file that is written with this
test. "Opening" the tape device means that it is logically connected to the system:

4350 OPEN 1,1,1, "Test-Tape 1"

Line 4360 is the beginning of a FOR-TO loop, in which I is equal to 1 through

100. This serves to write 100 records onto Test-Tape 1:

4360 FOR I = 1 TO 100

Line 4370 actually prints the record which will be written 100 times. The
PRINT #1 statement instructs the program to direct the output to file #1, which
is the cassette drive opened in line 4350. Its output is the character string 170,
which is a pattern with every other bit on: 10 101010.

4370 PRINT#1,CHR$(170):NEXT

At line 4380, the cassette drive is closed with the CLOSE 1 statement. It is
opened again immediately, and given a new file name of "Test-Tape 2."

4380 CLOSE 1:0PEN 1,1,1,"Test-Tape 2"

110 The Cassette Drive

Line 4390 begins another FOR-TO loop that goes from one to 100. This time,
it's output is character string 85, which is a pattern with every other bit off:
01010101.

4390 FOR I ~ 1 TO 100

4400 PRINT#l CHR$(85):NEXT

Once the FOR-TO loop is complete, line 4405 closes the cassette drive:

4405 CLOSE 1

Line 4410 prompts the user to rewind the tape, press PLAY, and press any
key to continue:

4410 PRINTPRINT "Rewind the tape and press PLAY"

PRINTGOSUB 3200

Line 4415 sends the program to line 4460, the beginning of the Read Test:

4415 GOTO 4460

When the user selects 2 from the Cassette Drive Diagnostic Menu, the Read-
Only Test is activated, beginning at line 4420. This test is also the second part
of the Write/Read Test. Line 4420 itself clears the screen with the Clear Screen
subroutine:

4420 GOSU B 2990

Line 4430 displays the title of the test, and the followi ng I ines print the necessary
user prompts:

4430 PRINT TAB(13) "Read Only Test":PRINT

4440 PRINT" Place the test tape in the cassette drive"
4450 PRINT "and press PLAY"
4455 PRINT:GOSUB 3300:GOSUB 3000:PRINT

Line 4460 opens the cassette drive device in a read mode, rather than a write
mode as in the first test. This is indicated by the 0 instead of a 2 in the second
operand. It is looking to read a file called "Test-Tape 1," which was created by
the Write/Read Test. This is also the point where the Write/Read Test branches
after it has completed writing the test files:

4460 OPEN 1,1,0,"Test-Tape 1"

Line 4470 is a FOR-TO loop for 100 records. Instead of writing information
to tape as before, it reads information from the tape, placing it into variable A$:
 Commodore Care Manual 111

4470 FORI=1T0100
4480 INPUT#1,A$

Line 4490 checks variable A$ for accuracy. If it is not equal to 170, which
was the value written to Test-Tape 1, error counter E is set equal to one. From
there, it is incremented with each error encountered through each pass of the
FOR-TO loop.
After A$ is compared, the program falls through to the NEXT statement at
line 4495, which sends the program back through another loop. This continues
until 100 passes have been completed:

4490 IF A$< >CHR$(170) THEN E=E+1

4495 NEXT

4500 closes the cassette drive device:

4500 CLOSE 1

Line 4510 immediately opens the device again. This time the program looks
for the Test-Tape 2 file created in the Write/Read Test:

4510 OPEN 1,1,0,"Test-Tape 2"

Line 4520 begins a FOR-TO loop, and again it reads from one to 100, inputting
its data into variable A$. This time it compares the data with character string val-
ue 85. If A$ is not equal to 85, the error counter is incremented as before:

4520 FOR 1=1 TO 100

4530 INPUT#1,A$
4540 IF A$< >CHR$(85) THEN E1 =E1 +1

Line 4550 sends the program back through the FOR-TO loop:

4550 NEXT I

Once the 100 passes through the loop are completed, line 4560 closes the
cassette drive:

4560 CLOSE 1:PRINT

Line 4570 displays the number of high value errors encountered during the
test, if any; while line 4580 displays the number of low value errors encountered:

4570 PRINT TAB(3) "There were" ;E;" High Value errors"

:PRINT
4580 PRINT TAB(3) "There were"; E1;" Low Value errors"
:PRINT
112 The Cassette Drive

Line 4590 goes to line 3200, which prompts the user to press any key to end
the test:

4590 GOSUB 3200

Finally, the program falls through to line 4600, which sends it back to line
50 to display the System Diagnostic Main Menu:

4600 GOTO 50
 Chapter 6
Tile Disk Drive
Computer data is broken down into a series of ON and OFF bits: ones and zeros.
Eight of these ON and OFF bits constitute a byte. Most computer dimensions are
in terms of bytes, particularly the amount of data that can be stored in system
memory, or the amount of data that can be stored on a diskette.
Every computer system unit is rated for a certain capacity of data it can store
at one time within system memory. The capacity of the Commodore 64 is 64
kilobytes of data (approximately 64,000 bytes), while that of the Commodore 128
is 128 kilobytes of data.
This capacity is not large enough to hold software programs and all your data.
Two or three application programs could easily use up this capacity, leaving no
room for additional software or data with which to use the programs. The disk
drive provides the additional storage necessary to supplement system memory.

DESCRIPTION AND FUNCTION OF THE DISK DRIVE

The disk drive provides a means for high-speed storage for programs and data,
and as such, it is one of the most useful peripheral devices you can use with the
Commodore (Fig. 6-1). With the disk drive, you can quickly store and access
programs such as spreadsheets, databases, and word processors. The disk drive
can also store the data on which these programs operate: the numbers and table
data in the spreadsheet, the field and record data in the database, and the words
in the word processor.
Throughout this chapter, the terms "disk," "diskette," "disk drive," and

113
114 The Disk Drive

"drive" are used. Disk is the generic term for the floppy disk media on which
the data is written . Diskette also refers to the floppy diskette media. Disk drive
and drive are both generic terms for the floppy disk drive.

Types of Disk Drives

The Commodore systems can accommodate two different types of disk drives.
The 1541 disk drive is a low-capacity drive which can store 175 kilobytes of data
on a diskette. The 1571 disk drive is a high-capacity drive which can store twice
as much: 350 kilobytes.
Both the 1541 and the 1571 are external disk drives; they reside in their own
housing external to the system unit, and use their own power supply (Fig. 6-2).
The first computers with disk drives were the mainframe computers used in
large corporations. The storage media used were 14-inch metal platters (Fig. 6-3).
These rigid platters, or disks, were stacked like phonograph records in the
mainframe's disk drive.
When the personal computer was invented in the seventies, a new kind of
storage disk was introduced: the eight-inch floppy diskette (Fig. 6-4). They were
called "floppy" because, unlike their metal predecessors, the recording media
consisted of a smaller platter made of thin, flexible plastic and encased in a
protective cardboard covering. The technology produced by the microcomputer
revolution miniaturized everything about the computer, including the disk drive.

Fig. 6-1 . The Commodore disk drive.

 Commodore Care Manual 115

- - . ~-

·--t'-t:

..
Fig. 6-2. The Commodore disk drive is external to the system unit.

The microcomputer's components continued to shrink in various ways. Among

these components were the disk drive and diskette_ Soon the 5%-inch floppy
diskette with its 5Y4-inch disk drive became the standard (Fig_ 6-5)_ These diskettes
were smaller and easier to use than the eight-inch versions_ The Commodore
systems use these 5%-inch floppy diskettes_

How a DIsk DrIve FunctIons

The disk drive attaches to the computer system unit by means of the disk
interface built into the Commodore system 's motherboard _ The serial bus
connector for this interface is located at the rear of the system unit and is where
the disk drive cable is connected_
Up to four disk drives can be daisy-chained together (Fig. 6-6). This means
that the first disk drive cable connects from the system unit to the first disk drive;
the second connects between the first and second disk drive; the third connects

Fig . 6-3 . The 14-inch mass storage platters.

116 The Disk Drive

Fig. 6-4. The eight-inch floppy diskette.

between the second and third, and so on. Having multiple disk drives provides
greater ease of use and versatility than just having one_
The disk drive includes a motor which spins the diskette at 300 to 400
revolutions per minute (rpm). The disk drive also consists of a head-arm assembly
which locates, reads, and writes data to and from the disk according to the
computer's internal program instructions (Fig_ 6-7).

Fig. 6-5. A 5%-inch floppy diskette.

 Commodore Care Manual 117

daisy chain

!
computer

Fig. 6-6. Disk drive daisy chain.

The diskette is a magnetic recording medium made with iron oxide, similar
to the material used on cassette tapes for a stereo cassette player. The magnetic
material covers the surface of the diskette like an emulsion, or film_ It is into this
material that data are written, stored, and read magnetically (Fig_ 6-8)_
The floppy diskette has a means for protecting the programs and data stored
there from being overwritten or erased_ The 5V4-inch diskette includes a small
cutout on the side called the write-protect notch. As long as the write-protect notch
is exposed, the disk drive is able to write information onto the diskette as well
as read from it (Fig. 6-9). New boxes of diskettes always include a package of
adhesive foil tapes. When one of these tapes is placed over a diskette's write-
protect notch, the disk drive's ability to write information onto the diskette is
"turned off." The tape blocks the write logic sensor in the disk drive, and no data
can be written onto this diskette.
When you insert your diskette into the disk drive and close the drive latch,
a switch inside the drive tells the system that a diskette has been inserted. The
drive motor then spins the diskette.
There is a small hole located near the center of the diskette. This hole is used

floppy diskette

Fig. 6-7. Disk drive head-arm assembly.

118 The Disk Drive

Fig . 6-8 . Data written on tile diskette

for timing and synchronization. The diskette must be spinning at about 300 rpm
to be in a ready state for reading or writing data. This timing and synchronization
hole is used as a means for sensing when the platter is spinning at the correct
speed. it is also used as a reference point, marking the start point for information
to be written on the diskette. When the disk drive comes up to speed, which
takes about a second, it is ready to read or write data.
Within the disk drive unit is a mechani,m referred to as the head. The head
is a magnetic device on the end of a mechanical access arm. The head can
magnetize the diskette emul sion, thereby writing new data onto the diskette. it
can also sense a magnetic pattern already in the emulsion, thereby reading existing
data. The head itself never physically touches the surface of the diskette as it reads
or writes . instead, it rides ct few microns ( a micron is one millionth of a meter)

Fig. 6·9. Write-protect notch.

 Commodore Care Manual 119

above the diskette on a cushion of air. Software and hardware logic position the
head at the proper location for reading or writing.
The diskette, like a phonograph record or a compact laser disk, stores specific
information in specific areas. Just as the laser disk might have different songs on
twelve different tracks, for example, a diskette has information stored on various
tracks and sectors.
The diskette is divided into a series of concentric circles. Each circle is a track.
There are 35 tracks on a 175-kilobyte 1541 disk drive, and 70 tracks on a
350-kilobyte 1571 disk drive. When the diskette is formatted, each track is divided
into sectors (Fig. 6-10).
Exactly one sector's worth of information is transferred in any given read or
write operation. Your program might need to manipulate only 20 characters of
that sector, but the computer always transfers all the information in the entire
sector. One sector on either of the Commodore disk drives contains 256 characters.
When a read command is issued by the operating system or the application
program, the disk drive positions the head at the proper track and sector. The
head copies the data from the sector and transfers it to a disk buffer. The program
logic extracts the record needed, and it is used as directed by the program.
A write command points to a disk buffer that contains the data to be written.
The head is positioned over the proper track and sector, and then the data are
transferred onto the diskette.

TROUBLESHOOTING AND REPAIR GUIDELINES

Disk drive problems can be caused by the diskette, the disk drive, or the
system unit/motherboard. To offset diskette problems, always maintain current
backups of your software programs and data.

Track _____...J
S e c t o r - - - - - - - - -J
Fig. 6-10. Diskette tracks and sectors.
120 The Disk Drive

If your troubleshooting efforts point to a problem in the disk drive, take it

in for servicing. The disk drive can require many precision adjustments that should
be performed by computer repair professionals. If a disk drive problem turns out
to actually be a problem with the motherboard, refer to Chapter 2 for system unit
troubleshooting procedures.

NOTE: While running the System Diagnostic Program, if the disk drive
encounters an error in writing or reading data, the error message is not
automatically displayed. A drive error is indicated by the drive's red LED
flashing on and off. If you see this condition, press RUN/STOP, then enter
GOTO 5180. This returns the system to the location in the Disk Drive
Diagnostic Module that displays the error code, the message, and the track
and sector wh ich contai ns the error.

Problem: The Disk Drive Does Not Work

If you insert a diskette into a disk drive but cannot read from or write
to it, try the following solutions.

L.--J Solutions

D Check how the diskette is inserted. If it's inserted upside-down, the drive cannot
read from or write to it. The diskette label should be face up.

D Make sure the diskette is formatted correctly for your system. For example,
a diskette formatted for a 1571 cannot be used on a 1541 disk drive. (Howev-
er, you can use a diskette formatted for a 1541 on a 1571 disk drive, although
it would not be the most efficient use of the drive, because the diskette is on Iy
formatted for half of its potential storage capacity.)

D Most disk drives have an indicator light next to the drive door. This light ei-
ther shows that the drive has power or that the drive is currently executing
a read or write operation. If the system boots up, the cursor is displayed on
the screen, and the fan is running, but you do not see the disk drive indicator
light come on, then there's a good chance that no power is being supplied
to the disk drive.

D The disk drive has its own power supply. First make sure that power is being
supplied to the drive. Check that the drive is properly plugged in. If it is, try
using a different electrical outlet. See whether the outlet being used for the
drive is controlled by a light switch.

D If the power checks out but the drive's indicator still does not light, there is
most likely a problem with the drive's power supply. Check the power supply's
fuse located on the rear of the disk drive (Fig. 6-11). Pull the fuse out by inserting
the end of a flatblade screwdriver into the fuse slot and turning it
counterclockwise until the fuse holder is disengaged. Examine the fuse. If it
is blown, replace it with another of the same rating. If the fuse is still good,
take the drive in for servicing.
 Commodore Care Manual 121

Fig. 6-11. Disk drive fuse location.

D If the operating system does not boot up, check that the disk drive interface
cable is properly attached between the drive and the CPU board in the system
unit.

D If your Commodore configuration includes more than one disk drive, there
might be a problem with the daisy-chain arrangement that could be preventing
the disk drive from getting power_ Each disk drive must have its own unique
address which is set internally in the drive itself. To set the drive's address,
follow these steps:
1. Turn off the disk drive.
2. Disconnect the cables from the drive.
3. Turn the drive upside-down.
4. Remove the four phillips screws from the bottom of the drive (Fig. 6-12).
5. Hold the case together and turn it rights ide-up again.
6. Remove the top of the disk drive housing.
7. Remove the two screws from the side of the metal housing shield (Fig.
6-13).
8. Remove the metal housing shield.
9. Locate the address jumper block on the printed circuit board (Fig. 6-14).
10. Refer to Table 6-1 to determine which jumper should be cut to give the
disk drive its proper address for its place along the daisy chain.
11. Use a small pair of diagonal wire cutters to cut the jumper(s) as needed.
12. Replace the metal housing.
13. Replace the upper case of the disk drive and reinstall the phillips screws.
14. Reconnect the disk drive cable.
15. Test the disk drive again to see if this solved the problem. If not, take
the drive in for servicing.
122 The Disk Drive

Fig. 6-12. Removing the drive screws.

Fig. 6-13. Removing the metal housing.

 Commodore Ca re Manual 123

(]DCD
P~ P2
cut trace with a
sharp knife

Fig. 6-14. Address jumper block

124 The Disk Drive

Table 6-1. Disk Addresses.

Device Address P1 P2

8 Intact Intact

9 Cut Intact

10 Intact Cut
11 Cut Cut

Problem: Cannot Read or WrIte to the DIskette

A common disk drive problem is that the system cannot read data from or
write data to a diskette. In this case, the first thing to check is the diskette itself.

[2' SolutIons

D If the system is not writing, and you are using a brand new diskette, first make
sure that it is the correct type of diskette for your drive. There are hard-sectored
and soft-sectored, single-density and double-density, single-sided and double-
sided diskettes.

D If the diskette is the correct type for the drive, the problem might be that the
diskette is not formatted. There are many diskette manufacturers, and the same
make of diskettes can be used with a number of different computer types. A
diskette is made to work on your particular computer by inserting the diskette
into the disk drive and running the operating system's format program. This
must be done to all new diskettes in order for them to work with your computer.
The format program places operating system information and a disk
directory program onto the new diskette. The format program also tests the
diskette for bad sectors. If any bad sectors are found, the format program blocks
them out. The diskette can still be used, and valuable data is prevented from
being written onto bad areas.

U If the system is able to read from a diskette, but cannot write to it, or if you've
run the Disk Drive Diagnostic Module and the 26 Write Protect On error
message was returned, look at the diskette and see whether it is write-protected.

[l If you've been using a particular diskette, and now find that the computer can
no longer read the data or write to it, it might have just worn out. Diskettes
are fragile, and after a great deal of use they can actually wear out, much the
same way that a phonograph record or cassette tape can wear out after
continuous use. This is one reason why keeping a current backup copy of each
diskette is so important. If a diskette wears out, and the message 25 Write Error
is displayed, simply use its backup diskette.

n If you still cannot read from or write to the diskette, try a different diskette,
one that you have recently used and know is not defective. If the system has
 Commodore Care Manual 125

no problem with this diskette, the original diskette you were trying to use was
defective. Use its backup.

D If you cannot read from or write to the second diskette, there might be a prob-
lem with the drive. To check this, try the diskette on another system. If it does
not read or write on that system, this indicates a bad diskette. However, if
it does read and write on the other system, your disk drive is probably faulty.

D To begin troubleshooting the disk drive, run the Disk Drive Diagnostic Module
on the suspected disk drive. The diagnostic writes a known pattern to the disk,
reads it back, and compares the two to make certain they match. This checks
the read/write logic.
When running the test, if two or three error messages are returned, a bad
sector on the disk is probably the cause. When a new diskette is formatted,
all bad sectors are blocked out. Sometimes a sector can go bad after formatting.
In this case, the disk can be salvaged with reformatting. Reformatting lets you
start over with a "fresh" disk, and will block out the bad sectors. Remember,
however, that when a diskette is reformatted, all data on it is erased. You cannot
reformat without losing the data on the diskette.
If the diagnostic test returns a lengthy series of read errors, either the disk
drive or the drive controller read circuit on the motherboard is probably faulty.
To check this, boot up the system and load the program from that disk drive.
If it boots up and loads satisfactori Iy, then the read logic on the motherboard
is fine. The problem lies in the disk drive, which should be taken in for
servicing.

Problem: Cannot load a Program or Read a Data File

If attempts to boot up the system only caused a read error message to be
returned, there could be a problem with the disk drive's read circuitry.

121 Solutions

D If the system includes a second disk drive, place the program diskette in that
drive, and try reading the program from there. If the system still cannot read
from the other drive, this indicates a bad program diskette. Load the backup
diskette.
If the disk drive does load, load the Disk Drive Diagnostic Module. Run
the diagnostic on the drive that would not load the program. If the test runs
successfully, and the successful test completion message is returned from the
diagnostic, then nothing was wrong with the disk drive. It was probably just
a problem with the diskette. Try a different diskette, and it should work.
If the diagnostic test fails, this indicates that the disk drive is defective,
and it should be taken in for servicing.
D If the system cannot boot up, read data from or write data to any of the disk
drives, then the problem almost certainly resides on the disk drive interface
circuit within the system unit, and not on the disk drive itself. Refer to Chapter
2 to troubleshoot the motherboard.
126 The Disk Drive

Problem: Head Crash

The disk drive head travels microns above the surface of the diskette to read
and write data. A head crash is the result of the head coming into contact with
the diskette. This can happen if the head is out of adjustment, a result of the disk
drive being shaken or dropped. A head crash can also be caused by contamination
on the disk or in the drive (Fig. 6-15).
If the head crashes, there is a grinding noise, and the disk is scratched. This
can be catastrophic to the disk and its data.
A head crash can be caused not only by a head being out of adjustment, but
also by a warped diskette. Diskettes, like records and tapes, can become warped
and damaged when exposed to heat or direct sunlight. If a warped diskette is
placed into the drive, it can scrape up against the head and cause a head crash.
Don't try to use a warped diskette, because if it does cause a head crash, the disk
drive will go out of adjustment and it will have to be taken in for servicing.
If the system cannot read from, write to, or format the disk, this indicates a
head crash. Another indication is a scratchy hissing sound heard when a diskette
is inserted into the drive.

B Solution

D When the head crashes, the drive must be taken in for servicing. Discard any
diskettes that have come into contact with the drive head after the crash.

Problem: Read Data Is Garbled

In addition to wearing out, diskettes can be damaged and the data on them
garbled if not handled properly. Because diskettes are magnetic media, magnetism
can adversely affect the data on a diskette. If you place a diskette next to a power
supply, or near an appliance with a motor, the motor's magnetic field could garble
the data.
Although the 5V4-inch diskette is enclosed in cardboard, there is a small
window at the hub of the diskette where the diskette is exposed for the drive
head access. If the diskette is handled roughly, or if this exposed area is
contaminated, the emulsion could be altered, and data lost.

fingerprint ridge
dust particle

read/write head j
rl --tie 0
diskette surface
Fig. 6-15. Diskette contamination.
 Commodore Care Manual 127

Problem: 20 Read Error

If the 20 Read Error message is displayed, this indicates that the disk drive
cannot locate the header portion of a sector that the system is trying to access.
This means that it's trying to access a nonexistent sector, or that the sector header
is damaged in some way. The sectors chain together, sector 1 to sector 2 to sector
3, and so forth. If sector 3 does not follow sector 2, for example, the system cannot
"find" sector 3. This could indicate either a defective diskette or a defective disk
drive.

~ Solutions

o Try to read a known, good diskette, perhaps the test diskette, in the same drive.
If the drive can read this diskette, it means the first diskette is defective. If
the drive still cannot read the diskette, it means the disk drive is probably
defective.

o Try to read the diskette in a different drive, if available. If the diskette can be
read in the different drive, it means the first drive is defective. If the diskette
cannot be read in the different drive, it means the diskette media is defective.

Problem: 21 Read Error

If the 21 Read Error message is displayed, the drive cannot find a sync mark-
er for the track that the system was trying to access. The sync marker is a starting
point for the diskette. It consists of data placed on the diskette by the formatting
process. This error indicates either that the diskette is not formatted, or that the
disk drive does not contain a diskette. The drive door might have been
inadvertently closed without the diskette being inserted.

B Solutions

o Check that there is indeed a diskette in the drive.

o Insert another diskette that you know is formatted, perhaps the test diskette.
Run the Disk Drive Diagnostic again. If the diagnostic runs without errors,
the original diskette probably was not formatted. If the diagnostic returns the
same error message, the disk drive might be out of alignment. Take it in for
servicing to have it realigned.

Problem: 23 Read Error

If the Disk Drive Diagnostic returns the message 23 Read Error, this indicates
a checksum error, which occurred when reading data into internal memory. A
checksum is a method by which the computer internally tests the information
to ensure that it has been read properly. A checksum is actually data that
accompanies the data being read. The checksum is used for comparison purposes;
it compares the data being read in from the diskette to the data that is being
transferred to system memory. This should be the same data. If it is not, then a
checksum error is returned.
128 The Disk Drive

B Solution

o If this error message occurs frequently, there is probably a problem with

grounding. Make sure that the diskette drive is properly grounded with a
grounded plug.

Problem: 24 Read Error

If the Disk Drive Diagnostic returns the 24 Read Error message, a hardware
error has occurred while the drive was reading data or header information from
the diskette into system memory.

:;:1 Solution

o This indicates a problem with electrical grounding. Make sure that the diskette
drive is properly grounded with a grounded plug.

Problem: 25 Read Error

If the Disk Drive Diagnostic returns the 25 Write Error message, there is a
data mismatch. When information from system memory is written to a disk, it
goes through a process called verification. In this process, the data being written
is immediately read back and compared to the data in system memory. If the two
sets of data do not match, this error message is returned.

V' Solution

o If this error occurs frequently on the same diskette, there is probably a disk
media problem. Using a backup of the diskette or a new diskette will solve
the problem.

Problem: 26 Write Protect On

If the 26 Write Protect On error message is returned while running the Disk
Drive Diagnostic, this indicates that the system is trying to write information onto
a diskette that is write-protected.

?1 Solution

o Remove the diskette from the drive, then remove the adhesive write-protect
tape from the edge of the diskette. Insert the diskette back into the drive, and
the system will now be able to write information onto the diskette. Remember,
however, that you probably originally placed the write-protect tape on the
diskette in order to protect data already written on it. Make sure the system
does not overwrite valuable data, now that you have write-enabled the diskette.

Problem: 27 Read Error

The 27 Read Error message indicates that a checksum error (see the earlier
discussion of the 23 Read Error) occurred while the drive was reading the header
of a particular sector.
 Commodore Care Manual 129

B Solution

[l Check the electrical grounding of the disk drive. Make sure that the diskette
drive is properly grounded with a grounded plug.

Problem: 28 Write Error

The 28 Write Error message indicates that after the drive had written data
to the diskette, it was not able to locate the sync mark for the next sector. This
can indicate a mechanical problem in the drive motor or with the head positioning
mechanism. This could also indicate an improperly formatted diskette.

B Solutions

n Try writing to another diskette that you know is formatted properly. Run the
Disk Drive Diagnostic.

D If the same error message reoccurs, the disk drive might be defective, and it
should be taken in for servicing.

Problem: 62 File Not Found

If the 62 File Not Found message is returned, this means that the drive could
not locate the file being requested.

B Solutions

D Run the Disk Drive Diagnostic on the diskette. If this message is returned again,
there is a problem with the diskette media itself.

D Run the diagnostic with a different diskette, preferably a new one. If the
diagnostic does not detect the error, this means the original diskette was
defective. If the error message is returned again, this means the disk drive is
probably defective, and it should be taken in for servicing.

Problem: 66 Illegal Track and Sector

If the 66 Illegal Track and Sector message is returned, this indicates that the
drive is trying to access a nonexistent track or sector on the diskette. This could
happen particularly if you indicate that the drive is a 1571 drive when it is actually
a 1541 drive. Because the 1571 has a higher capacity than the 1541, the test
evidently attempted to access a track and sector beyond the limits of the drive.

[?I Solutions

D Run the Disk Drive Diagnostic Test again and make sure that you specify the
proper drive and diskette type (1541 or 1571).

lJ If the error message is still returned, there might be a problem with the disk
drive. Swap the drive on another system unit. If the drive fails on another
system, it is defective and should be taken in for servicing.
130 The Disk Drive

D if the drive works on the other system, there is probably a problem with the
system unit. Swap a different disk drive onto the system. if the new drive does
not work either, refer to Chapter 2 to troubleshoot the system unit.

Problem: 74 Drive Not Ready

if the 74 Drive Not Ready error message is returned, it means that the drive
contains no diskette, or that the drive door is open. it could also mean that the
diskette is not formatted.

:2l Solutions

D Check to see if the drive contains a diskette.

D if it does, make sure the drive door is closed.

D if the error message persists, check whether the diskette is formatted or not.
The easiest way to do this is to try another diskette that you know is formatted.

PREVENTIVE MAINTENANCE
Floppy disk drives require a degree of preventive maintenance. Make sure
that the disk drive doors are closed when not in use. This prevents dirt and dust
from collecting on the disk drive head mechanism.
Dust can be a big enemy to the disk drive motors. Dirt can collect on the
head mechanism and cause the head to crash. Covering the system with a dust
cover protects disk drives from dust and dirt.
When moving the floppy disk drives, insert the cardboard "diskettes" into
the drives and close the doors. These protect the head mechanism from being
jostled, thereby preventing it from going out of alignment during transport.
Obtain a disk drive head cleaning kit from a computer store. insert the special
diskette, which is permeated with a cleaning solution, into the drive. Enter a read
command to cause the diskette to rotate. The read/write heads are then cleaned
as they pass over the cleaning diskette.

RUNNING THE DISK DRIVE DIAGNOSTIC MODULE

To run the Disk Drive Diagnostic Module, follow the instructions provided
in "Running the Diagnostic Program" in Chapter One. Then press D to initiate
the Disk Drive Diagnostic Module (Fig. 6-16).
This diagnostic checks the disk drive and media. It also tests the two main
functions of the disk drive: reading from and writing to a disk. it exercises the
entire disk, checking for many types of problems. if a problem is encountered,
the appropriate error message is displayed on the screen.
The Disk Drive Diagnostic Module can run on either the 1541 or 1571 disk
drive, and you are prompted to enter which one the system uses.
When running the test, it is best to use a freshly formatted, empty diskette.
if necessary, a diskette containing data may also be used, although this would
not constitute as thorough a test. The diagnostic module tests the data that it writes
onto the disk to fill it up, but it does not test data already stored on the diskette.
 Commodore Care Manual 131

Disk Drive Diagnostic

Which Drive Do You Want to Test-

Enter Drive Type 1-1541 2-1571

Fig. 6-16. The Disk Drive Diagnostic Module.

Because the information already residing on the disk is not tested, it cannot
be damaged or wiped out. However, as always, make sure you have complete
current backups of all programs and files, especially those residing on any diskette
bei ng tested.
In response to the prompt, indicate the number of the drive to be tested: 8
to 15. The diagnostic creates a file called TEST, and makes four distinct passes
through the disk.
The first pass writes a series of 254-byte records that contain a 254-character
string of CHR$ value 170. CHR$ value 170 is a character that has every other
bit on (10101010). The diagnostic writes these records throughout the entire disk.
Once the disk is full, the file is closed.
The diagnostic immediately begins the second pass through the disk, which
consists of reopening the file and rereading the data that were written during the
first pass. The read data are compared to CHR$ value 170. If there is a discrepancy
between what was written and what is now being read, an error message is
displayed on the screen.
When the second pass of the test is completed, the file is deleted. The third
pass consists of recreating the file, this time with a series of 254-character records
of CHR$ value 85, which has every other bit turned off (01 01 01 01). It completely
fills the disk up again with this alternate character record, just as it did before
with CHR$ value 170. When the diskette is full, the file is again closed.
CHR$ 170 has every odd bit turned off, and every even bit turned on. CHR$
85 has the opposite characteristics, with every odd bit turned off and every even
bit turned on. This creates an alternating bit pattern. Testing for alternating bit
patterns ensures that all possible bits on the disk are written.
lust as in the second pass, the fourth pass through the disk opens the file and
rereads the data written during the third pass. The read data are compared to CHR$
85. An error message is displayed if there is a discrepancy between what was
132 The Disk Drive

written and what is now being read. Then the file is erased, just as it was after
the second pass of the test.

HOW THE DISK DRIVE MODULE WORKS

When the user presses 0 or d from the System Diagnostic Main Menu, the
program branches to line 5000. A REMARK statement in the program marks the
beginning of the Disk Drive Diagnostic Module (Fig. 6-17).

5000 REM: "Disk Drive Diagnostic Module"

Lines 5010 and 5020 initialize two variables, HV$ for high values, and LV$
for low values. HV$ builds a string of the high CHR$ value 170. The loop continues
eight times, essentially building an eight-character record:

5010 FOR 1~1 TO 8:HV$~HV$+CHR$(170)NEXT

5020 LV$~"":FOR 1~1 TO 8:LV$=LV$+CHR$(85):NEXT

Line 5020 does the same thing, building a string of the low CHR$ value 85 eight
times.
Line 5030 clears the screen and displays the diagnostic title. Line 5035 then
displays a prompt for the user to enter the disk drive to be tested. The user would
enter a value such as 8 to designate the first drive, 9 to designate the second drive,
or any drive designation up through 15. This drive designation number is placed
in variable D:

5030 GOSUB 2990:PRINT TAB(10)"Disk Drive Diagnostic":PRINT

5035 INPUT "Which Drive Do You Want To Test";DPRINT

Line 5036 checks that a valid drive number selection has been made. If an
invalid drive number has been entered, the program displays an error message
and loops back to line 5035 for the user to try again:

5036 IF 0<8 OR 0> 15 THEN PRINT "Invalid Disk Number":

GOTO 5035

Line 5037 prompts the user to specify the drive type. A value of one indicates
the 1541 drive, and a two indicates the 1571 drive. If a value other than one
or two is entered, line 5038 causes the program to default to the 1541 drive:

5037 INPUT "Enter Drive Type 1-1541 2-1571";T

5038 IF T < > 2 THEN T ~ 1

Line 5040 sets variable BF$ equal to HV$. The name variable NM$ is
initialized to the character literal "High Values":

5040 BF$=HV$:NM$~"High Values"

 Commodore Care Manual 133

5000 REM: "Disk Drive Diagnostic Module"

5010 FOR 1=1 TO 8:HV$=HV$+CHR$(170):NEXT
5020 LV$="":FOR 1=1 TO 8: LV$=LV$+CHR$(85):NEXT
5030 GOSUB 2990:PRINT TAB(10)"Disk Drive Diagnostic":PRINT
5035 INPUT "lIhich Drive Do You lIant To Test-";D:PRINT
5036 IF D<8 OR D>15 THEN PRINT "Invalid Disk Nurrber":
GOTO 5035
5037 INPUT "Enter Drive Type 1-1541 2-1571";T
5038 IF T<>2 THEN T=1
5040 BF$=HV$:NM$="High Values"
5050 FOR 1=1 TO 2
5060 OPEN 1,D,2,"TEST,s,w"
5070 PRINT:PRINT"lIriting ";NM$;" to Disk"
5072 IF T=2 THEN Z=33600
5074 IF T=1 THEN Z=16800
5075 FOR A=1 TO Z
5077 B1$=""
5080 PRINT#1,BF$
5090 NEXT A
5095 CLOSE 1
5100 OPEN 1,0,2, "TEST,s,r"
5110 PRINT "Reading ";NM$;" from Disk":PRINT
5115 FOR A=1 TO Z
5120 INPUT#1,B$
5140 IF B$<>BF$ THEN PRINT "Error Reading ";NM$:E=E+1
5150 NEXT
5160 CLOSE 1
5165 OPEN 15,8,15,"sO:TEST":CLOSE 15
5170 BF$=LV$:NM$="Low Values":NEXT I
5180 PRINT:PRINT "There were ";E;" errors encountered"
5182 OPEN 15,8,15:INPUT#15,DS,DS$,T,S:PRINT:PRINT DS;
II,",DS$+",";T;II,";S:PRINT
5183 CLOSE 15
5185 IF EX=1 THEN RETURN
5190 GOSUB 3200
5200 GOTO 50

Fig. 6-17. The Disk Drive Diagnostic Module listing.

When the diagnostic is running, the words High Values are displayed on the
screen, indicating that it is currently writing $CHR$ character 170 to disk.
Line 5050 is the beginning of a FOR-TO loop. The test runs through two
passes: one for the high values of $CHR$ value 170, and one for the low values
of $CHR$ 'value 85.
134 The Disk Drive

5050 FOR 1=1 TO 2

The FOR-TO loop allows the same code to be used in both cases, simply inserting
the different variables as appropriate.
The program proceeds to line 5060. The disk file is opened using the disk
number that was stored in variable D in line 5035. The file is named "TEST,"
and is opened in the output mode as a sequential file:

5060 OPEN 1,D,2, "TEST,s,w"

Line 5070 prints a blank line and then displays an informational message
indicating that the contents of NM$, which was initialized in line 5040 to "High
Values," is being written to disk:

5070 PRINT:PRINT"Writing ";NM$;" to Disk"

Line 5072 determines the number of records to write, based on the value
of T. If T equals two, then variable Z is set to 33600, which fills up all available
free sectors on a 1571 diskette. Otherwise, Z is set to 16800, the number of eight-
byte records needed to fill up the sectors available on a 1541 diskette:

5072 IF T =2 THEN Z=33600

5074 IF T = 1 THEN Z= 16800

Line 5075 causes 33600 or 16800 records to be written to the dsk. This
completely fi lis up the diskette:

5075 FOR A= 1 TO Z
5077 B1$=""

Line 5080 is where the actual output to disk takes place. The PRINT #1
statement from variable BF$ writes the high values out to the disk:

5080 PRINT#1,BF$

Line 5090 is the NEXT statement which serves to loop the program back to the
Write Test code:

5090 NEXT A

Line 5095 closes the file after all records have been written:

5095 CLOSE 1

Line 5100 reopens TEST, which is the name designated for the file created in
the Write Test:
 Commodore Care Manual 135

5100 OPEN 1,0,2, "TEST,s,r"

Line 5110 displays the message indicating that the high values of NM$ are being
read from the disk:

5110 PRINT "Reading ";NM$;" from Oisk":PRINT

Line 5115 begins a FOR-TO loop which causes the program to read the 33600
or 16800 records, depending on the drive type:

5115 FOR A = 1 TO Z

Line 5120 inputs the data being read from the disk into variable B$:

5120 INPUT#1,B$

When all the data have been read, the program branches to line 5160 to end
the test.
If the end-of-file has not yet been reached, the program falls through to line
5140, which compares variable B1 $ to variable B$. B1 $ contains the high values
read from the disk in line 5120, while B$ contains the high values written into
the disk in line 5080:

5140 IF B$< >BF$ THEN PRINT "Error Reading ";NM$:E=E+1

In other words, this statement compares the data that was written in the Write
Test to the data that was read in the Read Only Test. They should be exactly the
same. If there is a discrepancy between the two, a message is displayed, indicating
a high-value error reading.
The latter part of the statement, E = E + 1, increments an error counter. This
counter keeps track of the number of read errors encountered during the test.
The program proceeds to line 51 50, a N EXT statement to increment the FOR-
TO loop begun in line 5115:

5150 NEXT

There was an end-of-file trap at line 5130. When the end of the file is reached,
the program branches here to line 5160 to close the test file:

5160 CLOSE 1

The CLOSE 1 statement closes the disk drive.

Line 5165 erases the high-values TEST file from the disk drive:

5165 OPEN 15,8,15,"sO:TEST":CLOSE 15

136 The Disk Drive

Line 5170 sets BF$ to CHR$(85) and reads the disk for the low values:

5170 BF$=LV$:NM$="Low Values":NEXT I

Once the FOR-NEXT loop is completed, the program proceeds to line 5180.
Line 5180 displays a summary of the number of read errors encountered during
the test, such as "There were 2 errors encountered," or better yet, "There were
o errors encountered:"
5180 PRINT:PRINT "There were ";E;" errors encountered"

If read errors are returned, there could be a problem with either the diskette or
the disk drive itself. Refer to "Troubleshooting and Repair Guidelines" earlier
in this chapter for further action.
Line 5182 displays the error code, error message, faulty track and sector for
any error encountered in the course of this test:

5182 OPEN 15,8,15:INPUT#15,OS,OS$,T,S:PRINT:PRINT OS;

"," ,OS$+" ,";T;",";S:PRINT
5183 CLOSE 15

If a read or write error takes place during this test, the error message does not
display automatically. Such an error is indicated by the disk drive light flashing
on and off. If this happens, press the RUN/STOP key on the keyboard, then enter
GOTO 5182. The System Diagnostic Program resumes at this point, and line 5182
displays the error message and information.
Line 5185 checks for the EX flag. If it equal to one, this indicates that the
Exerciser Module is in effect, in which case the program returns to the Exerciser
Module portion of the code. If it is equal to zero, the program falls through to
line 5190:

5185 IF EX=1 THEN RETURN

Once the test is complete, it prompts the user to enter any character to
continue and then branches back to line 50, the beginning of the System Diagnostic
Main Menu:

5190 GOSUB 3200

5200 GOTO 50
 Chapter 7
Tile S.ri I
Co _ nic lion
In rface
With the proper equipment, the Commodore can "talk" to many other devices:
a modem, a printer, a mouse-even another computer. Data and information can
be sent to and received from these peripherals. Communicating among different
devices requires the services of the serial communication interface.

DESCRIPTION AND FUNCTION OF

THE SERIAL COMMUNICATION INTERFACE
The serial communications port is a 25-pin edge connector located on the
back of the Commodore system. An additional interface, such as the VIC-MODEM
or Commodore RS-232 cartridge, must be plugged into this connector in order
to use the port as a modem or printer interface.
The interface reaches the outside world by means of a cable to the other de-
vice with which communication is to take place. It is through this cable that the
appropriate signals and data are passed to and from the other device.

Types of Serial Communication Devices

The Commodore serial communication interface is used to communicate with
devices such as the modem, printer, and another computer.

Interfacing with a Modem. The modem is a device widely used for serial
communication. It allows transmission and reception of computer data using

137
138 The Serial Communication Interface

telephone lines. The word modem is derived from the term modulator-
demodulator. The computer produces data and control signals in the form of
electrical impulses, also known as digital signals. These digital data exist in the
form of ONs and OFFs, or ones and zeros.
The modem converts this digital signal into sound waves, or analog signals
for transmission over telephone lines. This part of the conversion is referred to
as modulation.
The modem at the receiving end then converts the analog signal back into
a digital signal, and this part of the conversion is referred to as demodulation.
The information once again takes the form of ones and zeros, so the computer
connected to the receiving modem can successfully interpret it (Fig. 7-1).
Modems can only operate in pairs. For two computers to communicate with
one another, each computer must be connected to a modem that has matching
configurations. This would include communication speed, data size, start bits,
and other parameters that are discussed later in this chapter.
Online services such as CompuServe, DElPHI, Dow Jones News, The Source,
and Computext make it easy for people with computers and modems to link up
to the networks' centers of information. By coupling the modem to a telephone,
then dialing a specific telephone number (which is often a local or toll-free
number), the Commodore can be linked into a network's mainframe computer.
You can then use the network service to research a wide range of information,
as well as to communicate with other users. Online services can also provide
banking, shopping, and airline reservation services through the use of the
Commodore's serial communication interface and the modem (Fig. 7-2).
The Commodore systems have two different types of modems available. One
is the RS-232 modem, and the other is the VIC-MODEM. The VIC-MODEM
connects into one of the game ports on the right side of the system unit. An RS-232
modem uses the RS-232 cable, and connects to the serial port at the rear of the
system unit.

Interfacing with a Printer. The serial bus interface is most commonly used
for the printer on a Commodore system. A serial bus is a daisy-chained, high-

Fig. 7-1. Modem communication.

 Commodore Care Manual 139

~~
Dow Jones News Service

'\ , ------------- f
~~
Users Groups
.=-~ Database Access

~
OJ / Mainframe
Computer OJ
~
Airline Reservations
~
Online Banking
Fig. 7-2. Online services.

speed serial interface. It is located on the back of the Commodore system unit,
and allows daisy-chaining of up to eight devices. It is used to interface disk drives
and Commodore-supplied printers.
However, if you have a serial pri nter using the serial communication interface,
it would be cabled to the serial communication port instead of the serial bus port.
The printer is typically attached to the computer with an interface cable, or hard
wire.
Just like with the modem, either type of printer must be configured with the
same data speed and size parameters that are set within the Commodore. This
is because the printer must know what to expect from the computer, and how
to handle it.
In some cases, the printer can even be used in conjunction with the modem
to provide long-range printing. A central computer from a remote site can send
information via a communication line, and have it print out on this local printer.

Interfacing Directly with Another Computer. If your Commodore resides

in an environment in which there are computers in relatively close proximity (less
than 50 feet), these computers can be hard-wired together with an interface. In
other words, they can be connected with a cable through their serial
communication ports to exchange data just as they would if they were hooked
up through modems. The difference is that phone lines are not needed in a hard-
wire connection because of the close proximity of the computers.
When computers are hard-wired together, data can be sent much faster. As
always, the communication parameters between the two computers must match
140 The Serial Communication Interface

in order for them to understand and process the information being sent and re-
ceived.
Hard wiring works over short distances of less than 50 feet. Communication
over longer distances requires modems or signal amplifiers, because the electrical
pulses diminish and are lost due to the resistance of the wire through which the
signals are traveling.

How the Serial Communication Interface Functions

Serial communication is a function of timing and speed. Several factors
contribute to keeping the communicating devices synchronized with one anoth-
er so that they can interpret the data being sent. Such factors include
communication software, data speed, data size, start and stop bits, parity, protocols,
and the interface port itself.

Communication Software. In order to use the serial communication interface,

communication software that works from the serial communication interface is
needed. An example of this kind of software is a modem communication program.
If you subscribe to an online network service such as Dow Jones, The Source,
or CompuServe, their user guides explain the communication software packages
that work properly with their devices.
Communication Parameters. Because data is sent one bit at a time in serial
communication, certain parameters must be specified when first setting up
communication software. These parameters pertain to data transmission speed,
the size of the data characters being sent, whether start and stop bits are employed,
and whether parity error-checking is to take place. These variables serve to
coordinate the communication and ensure that the data transfer is successful. The
particular variables used depend on the device with which the computer is
communicating. Online service user documentation details the particular
parameters needed.
The printer, modem, or other device with which the Commodore is going
to communicate must have the communication interface variables set identically
on their end in order for the communication link to be established and maintained.
These parameters are set either through the software or with switches on the
communication interface board. Check the device documentation for specific
details.
When you are running communication software for the first time, access the
setup mode to set the communication parameters. Once these parameters are set,
they can usually be stored on the program disk so that they are automatically
set each time the program is used.

Baud Rate. The first parameter pertains to how fast the device sends
information. The device receiving the data must know the speed at which the
data are being sent in order for the two devices to be in sync with one another.
In serial communication, speed is expressed in a measurement called baud.
Baud is usually the number of bits that can be transmitted in a second. The
 Commodore Care Manual 141

differences in baud rates are analogous to the different ways a car horn might
be sounded. Three short beeps can be heard much faster than three long beeps.
In the same way, eight bits of data traveling at 2400 baud are transmitted
and received much faster than the same eight bits traveling at 300 baud. When
the baud rate is set to a predetermined speed of which both devices are aware,
the system knows how long each ON bit lasts, and how long each OFF bit lasts.
Most communication interfaces for personal computers have a baud rate of 300
or 1200 bits per second.
Higher-speed communication, in the range of 4800 and 9600 bits per sec-
ond, is available, but is used primarily for communicating with devices that are
hard-wired to a system through an interface cable. A hard-wire setup does not
require an intermediary such as a modem in order to establish communication.
A printer, or even a computer that is hard-wired to another computer, is able to
operate at the faster speeds. There are modems available that can run at such
high speeds, but they are prohibitively expensive, especially for the small busi-
ness or home user.

Data Size. Another parameter, data size, refers to the size of the data being
sent: how many bits make up a standard character or word. A standard character
of data consists of seven or eight bits, depending on the software. The software
needs to know the character length or word length of the data being sent, so that
it knows what to expect (Fig. 7-3).

Start Bits and Stop Bits. In serial communication, the software adds additional
bits to each character to help coordinate the communication transfer. These added
bits are referred to as start bits and stop bits. When the software adds the start
bit and stop bit, then nine or ten bits are actually sent for each data character.
The start bit signals the beginning of a character, and captures the receiving
device's attention. It tells the device to expect seven or eight more bits of data
for processing. Likewise, the stop bit signifies the end of a character.
Both ends of the communication line need to know whether start bits and
stop bits are being employed, and if so, how many there are, one or two or each
(Fig. 7-4).

Parity. Another variable that many systems use is parity, which is an error-
checking scheme used to ensure accurate data transmission. With parity, the last
bit in a data word is set so that the sum of the number of bits is either an odd
number (for odd parity), or an even number (for even parity).

Word or Character
I;
r,11 0 001
Word Length is 8 Bits
Fig. 7-3. Bits, characters, and words.
142 The Serial Communication Interface

Stop Bit
Parity Bit (Odd Parity)
Start Bit - - - t

Fig. 7-4. The stop bit, start bit, and parity bit.

For example, if the system is set up with odd parity from the modem to the
computer, and a character or word is received with an even number of bits, parity
is not correct. This might mean that one of the character bits has dropped off during
transmission. A failure of parity indicates an error in transmission, and the
communication software either prompts you to try the data transmission again,
or it restarts it automatically for you.

Directionality. Depending on the device with which the Commodore is

communicating, the data might be sent in one direction only, or data might be
sent in both directions-to and from both devices. Printers are unidirectional
devices, meaning they only receive data; they cannot transmit data back to the
computer. When two computers are linked up through modems, on the other
hand, the data is said to be bidirectional, because data can be sent and received
to and from both systems.
Whether the data is unidirectional or bidirectional depends on the type of
device to which the data is being sent, as well as the software being used for
the communication transfer. Some parameters in the support software might need
to be set. There might also be switches to set on the serial communication interface
on the motherboard. This is detailed in the device documentation.

Emulation. Different types of computers have different keyboard control

sequences, keyboard mapping, screen format display, text handling, and special
functions. These aspects of unique computer design can hinder effective
communication between two different computers.
To solve this problem, an emulation program in the communication software
can disguise the Commodore and make it "pretend" that it is another computer
of a different design. The DEC VT100 is a common emulation mode, available
with communication software, in which the Commodore can emulate the VT100
terminal. When both computers are set up in the same emulation mode, then
all code sequences for the keyboard and monitor function as expected.
Protocols. The XONIXOFF protocol works in conjunction with the emulator,
and is set with the other communication software parameters. You can indicate
whether or not this protocol is to take effect. Even though the baud rates might
be compatible, if the receiving system cannot process the data fast enough, some
data could get lost. The XON/XOFF protocol places transmission "on hold" to
prevent the communication buffers from overflowing, and then turns it on again
to make sure that data is completely transferred.
For example, suppose your Commodore has a 2000-byte communication buf-
 Commodore Care Manual 143

fer. In the process of receiving a file that may be 16,000 bytes long, the commu-
nication buffer is quickly filled up. When this happens, the Commodore sends
a "suspend" command to the other system, temporarily stopping communica-
tion transfer. This suspension is the XOFF command. When the buffer is emptied
through computer processing, such as displaying characters on the screen, the
Commodore sends a "resume" command, which is XON. The transfer then con-
tinues where it left off. This process continues throughout the file in 2000-byte
chunks until all 16,000 bytes are successfully transferred.
There is another protocol used by modems to establish communication. This
is called the handshaking protocol. The handshaking protocol is analogous to
human greeting and communication protocols. When two people meet, they
ordinarily greet one another in the following manner:

"Hello, how are you dOing?"

"Hello, I'm doing fine. How are you?"
"Fine. Nice weather we're having today, isn't it?"

Then they might go on their way, or they might continue talking. The important
thing is that they have satisfied the human protocol of "the greeting." People
use such protocols in order to enhance their personal communication, and ensure
understand i ng.
If one person talks much faster than the other is able to comprehend what
is being said, there will be a breakdown in communication: words will be missed,
and the original thought will be misunderstood.
The manner in which protocols are used is important as well. If two people
meet, and follow the protocols, but in the wrong order, they might still have a
communication failure, as in this example:

"Good-bye. Nice weather we're having today."

"I'm fine, and you?"

When a person says "good-bye," our protocol implies that this is the end of the
conversation. If more is said after this end-of-conversation message, then there
will be confusion and lack of understanding.
The modem handshaking protocol operates under the same principle. Many
signals are used to establish modem communication. The following is a listing
of the handshaking protocol used to establish and maintain communication.

1. Run the program.

The TR (Terminal Ready) signal is issued.
2. Dial the phone.
Switch into data mode, DSR (Data Set Ready).
3. The other system answers and then sends the carrier signal.
The CD (Carrier Detect) light is illuminated on the modem panel.
4. You press a key to send a character code to the other system.
The RTS (Request to Send) signal is sent to the modem and the appropri-
ate light is illuminated.
144 The Serial Communication Interface

5. The modem tells your system that it is prepared to accept data for
transmission.
The CTS (Clear to Send) signal is sent to your system.
6. The data is sent.
The SD (Send Data) light is illuminated on the modem.

Interface Port. The serial communication interface board has a physical

connection, or port, into which a cable is attached. This physical connection is
where the functional signals and data are passed across the interface, one bit at
a time, between the two communicating devices.
As explained in Chapter 4, the serial communication interface sends seven
or eight bits of data "single file." The functional signals ensure that both machines
are synchronized with one another, and that they are prepared to receive or send
data. They also help detect breaks in the communication line and other
communication errors, and send back error signals to the programs when
necessary.
The RS-232 serial communication standard determines what the functional
signals consist of, and which cable wires carry which type of signal or data.

TROUBLESHOOTING AND REPAIR GUIDELINES

Establishing communication between two devices requires a balance of
software and hardware requirements. The software parameters and hardware
components must be set up and functioning properly on both ends of the
communication line in order for data to be sent, received, and read correctly.
The communication interface is located on the back of the system unit. It
derives its power from the system unit's power supply. Because of this, the prob-
lem of the communication board simply not working never occurs, unless of course
the system unit as a whole is not working.
There are two possible serial communication problems. The first is that
communication is not established. The second is that the results of communication
are garbled or incorrect in some way.

Problem: Communication Cannot Be Established

The inability to establish communication might manifest itself in not being
able to dial up, not being able to make the connection after dialing, or not being
able to detect the carrier after connecting.

o Solutions

o Check that the cable is properly connected and seated to the system unit serial
communication interfclce port.

o Make sure that the proper interface cable is connected to the serial
communication interface. The serial communication interface is usually a male
connector, meaning it is a pins-type connector.
 Commodore Care Manual 145

D Run the Serial Communication Diagnostic Module (described in the following

section of this chapter). If the test fails, and the character entered is not echoed
on the screen, try the test using another serial cable.

D Swap the VIC-MODEM or RS-232 cartridge on another Commodore system.

If it works, the problem is with the serial communication port on your
Commodore. Refer to Chapter 2 for instructions on cleaning the edge
connector. If it still does not work on your system, take the system unit in
for repair.
If the VIC-MODEM or RS-232 cartridge does not work on another system,
the problem lies in the modem/cartridge. Either take it in for repair, or replace
it.

D If the Serial Communication Diagnostic Module checks out, reload the

communication program and make sure that the parameters are set correctly.
Is the baud rate set correctly? Was the appropriate character or word size
specified? Is the other system expecting a parity bit to be enabled?

D Check the device with which you're trying to communicate. If it's another
Commodore, run the diagnostic program on it to see whether its
communication interface is working properly.

D Check the interface or system technical manual to see if the interface cable
has any special requirements. RS-232 is a relatively loose standard. Some cable
manufacturers use a different scheme for their RS-232 cable pins. These cables
might expect data from different pins, look for other signals, or have signals
tied together. If this is the case, cable that has the correct pin configuration.

D Most modems provide additional assistance with troubleshooting, usually

through a row of red indicator lights across the front status panel (Fig. 7-5) .
If your modem includes such an indicator panel, check that certain signals
are functioning. For instance, when the modem is properly cabled into the
Commodore, and the communication software is being run, the I ights over
TR and DSR should be illuminated. These lights indicate that the computer
and the modem are ready and that the interface signals are turned on and ready

Fig. 7-5. Modem status panel.

146 The Serial Communication Interface

to talk to each other. If these indicator lights are not on, there might be a prob-
lem with the interface cable connection or with the modem.
When data are being sent, the indicator lights over RO ("receive data")
or TO ("transmit data") are illuminated. When a key is pressed, these lights
indicate that the data for the key code are indeed being sent.

o The modem might also have a test mode (check the modem documentation
to see if this is the case). This test mode loops a data pattern back through
the modem. It takes a pattern of characters from the computer, sends the pattern
through the modem back to itself, and then returns the pattern to the computer.
This internalloopback test checks the modem to make sure that it is sending
and receiving as it should. Use this test mode if communication still cannot
be established. It helps troubleshoot one suspected modem problem at a time.

r:] A carrier is a tone that the modem expects before it can send data. It's like
saying "Hello" when the phone rings and you pick up the receiver. After saying
"Hello," communication can be established, and information from the caller
can be transmitted.
This carrier can be heard when using a smart modem that dials the phone
automatically. You would first hear the telephone ring through the modem
speaker, and then a high-pitched tone would sound. This audible signal is the
carrier, and it tells the system that the modem is ready to accept data, either
from your system or from the other system. The CO ("carrier detect") light
is illuminated. This indicates that the other system has answered and been
given the carrier.
If the carrier signal is not received, it could mean a wrong number, a busy
signal, or some other problem at the other end.

Problem: CommunIcatIon Results Are Garbled

Garbled data indicates that communication has been established, but there's
a problem with the data coming through the lines. This usually has to do with
one of the parameter settings, such as the word size or parity. Return to the
communication software parameter setup mode, and check all the settings.

~ SolutIon

o If you get a mixture of garbled characters and good characters-for example,

the word "login" is sent, but "Ioxxn" is received-you probably have a poor
telephone connection. Hang up and redial.

Problem: PrInter Does Not Work

If the serial communication interface connects with a printer, make sure that
the printer's internal switches are set up to conform to your configuration. Most
printers can communicate across either a serial or a parallel interface.

M SolutIons

n Printers ordinarily default to the parallel interface, and a switch must be set
 Commodore Care Manual 147

in order to use the serial communication line. Refer to the printer

documentation.

D The printer also needs to know the usual communication parameters, such
as the baud rate being run, the character length, the parity, and so forth. This
is set up with a DIP-switch in the printer interface board. The printer
documentation details how to make the necessary settings.

RUNNING THE SERIAL

COMMUNICATION INTERFACE DIAGNOSTIC MODULE
The Serial Communication Diagnostic Module initializes the serial
communication interface for testing. It sends a character through the interface,
loops it around, and displays it again on the screen. It checks that the interface
address is working properly, that the interface itself is working properly, and that
the system is receiving the same data that it is sending through the communication
loop.

NOTE: The Serial Communication Diagnostic Module works only with an

RS-232 modem, not the VIC-MODEM.

To run the Serial Communication Diagnostic Module, follow the instructions

provided in "Running the Diagnostic Program" in Chapter 1. Then press S to
initiate the Serial Communication Diagnostic Module.
Take the end of the cable that would connect to the peripheral with which
you want to communicate. In the connector at this end, attach a wire between
pins 2 and 3 (Fig. 7-6).
Pin 2 is the Receive data line, while pin 3 is the Transmit data line. Placing
a wire bridge or jumper across these two pins causes the data that is sent out
to be looped back and received. In other words, any character that is pressed
at the Commodore keyboard is sent out to the device, immediately received in
through these pins and sent back to the computer, and the character is echoed
back and displayed on the screen (Fig. 7-7).

. .................

Fig. 7·6. Wire bridge across pins 2 and 3.

148 The Serial Communication Interfac"!

. . . . . .. . . .
Pin 2
Receive Data

Pin 3 - - - - '
Transmit Data
Fig. 7-7. Loopback diagram.

There are plugs available that already have pins 2 and 3 wired together. Such
a plug is called a "2S-pin serialloopback connector," and can be purchased at
a computer or electronic supply store. The plug fits directly onto the serial port,
and accomplishes the same loopback test (Fig. 7-8).
The instructions to the Serial Communication Diagnostic Module appear on
the screen (Fig. 7-9). The Serial Communication Diagnostic consists of a single
test: the Display Character Loopback Test. You enter a character on the keyboard,
and it is sent through the communication loop created by the loopback wire. The
loopback causes the character to be immediately sent back and received as output
displayed on the monitor screen. This checks the functions of the serial
communication interface by both transmitting and receiving data .

• • • • • • • • • • • • •
• • • • • • • • • • • •
•
Fig. 7·8. Loopback connector.
 Commodore Care Manual 149

Serial Communication Diagnostic

Press CLR/HOME to End Test

press any key to continue

Fig. 7-9. Serial Communication Diagnostic instructions.

HOW THE MODULE WORKS

Pressing S from the System Diagnostic Main Menu causes the program to
branch to line 6000, where the Serial Communication Diagnostic Module begins
(Fig. 7-10).
Line 6000 begins by clearing the screen and positioning the cursor at the
HOME position, and is followed by the REMARK statement indicating that this
is the Serial Communication Diagnostic Module:

6000 GOSUB 2990:REM "Serial Comm Module"

Line 6010 prints the title of the diagnostic on the screen:

6010 PRINT TAB(3) "Serial Communication Diagnostic":

PRINT

Line 6020 prints the user instruction to press the CLR/HOME key to end the test:

6020 PRINT TAB(7)"Press CLR/HOME to End Test":PRINT

Line 6025 then instructs the user to enter any key to continue, once the previous
messages have been read:

6025 GOSUB 3300

150 The Serial Communication Interface

6000 GOSUB 2990:REM "Serial Corrm Module"

6010 PRINT TAB(3) "Serial COOITlJnications Diagnostic":
PRINT
6020 PRINT TAB(7)"Press CLR/HOIolE to End Test":PRINT
6025 GOSUB 3300
6030 GOSUB 3000:GOSUB 2990
6040 OPEN 2,2,3,CHR$(6)+CHR$(0)
6050 GET #2,A$
6060 IF A$="" THEN 6070
6065 PRINT A$:
6070 GET A$:IF A$="{CLR/H~E)" THEN 6100
6075 IF A$="" THEN 6050
6080 PRINT#2,A$;:GOTO 6050
6100 CLOSE 2:GOTO 50

Fig. 7-10. ihe Serial Communication Diagnostic Module listing

When the user presses a key, the program goes to line 6030, which clears
the screen again:

6030 GOSUB 3000:GOSUB 2990

Line 6040 opens the serial communication interface, which is designated as de-
vice #2. There are two character strings: 6 and O. These character strings establish
parameters for the serial communication line being opened. The first character
string, 6, indicates that the test is to be run at 300 baud, which is a sufficient
speed for this test. The second character string, 0, specifies that no parity checking
is to take place.

6040 OPEN 2,2,3,CHR$(6)+CHR$(O)

The GET instruction in line 6050 opens the receive side of the serial
communication interface, and places the character residing in the receive buffer
into variable A$. This prepares the program for testing.

6050 GET #2,A$

Line 6060 checks whether there is a value in A$. If there is none, and A$ is a
null, the program goes to line 6070 to get a value:

6060 IF A$ ="" THEN 6070

Line 6065 prints the value contained in A$ on the screen:

6065 PRINT A$:

 Commodore Care Manual 151

The GET statement in line 6070 causes the program to go to the keyboard
and look for the user's keystroke. This keystroke is placed into variable A$. If
this keystroke is the CLRlHOME key, the program branches to 6100, where the serial
communications interface is closed and the test ended:

6070 GET A$:IF A$="{CLR/HOME}" THEN 6100

If A$ does not contain the CLRlHOME key, the program continues with testing
the keystroke, falling through to line 6075. If A$ contains nothing, the program
branches from line 6075 to line 6050:

6075 IF A$= '"' THEN 6050

If A$ contains a keystroke other than CLRlHOME, line 6080 outputs it to the

serial communication interface, which has been defined as device #2:

6080 PRINT#2,A$;:GOTO 6050

Once A$ is output, the program returns to line 6050 to accept additional values
for testing.
Line 6100 closes the serial communication interface which was designated
as device #2. Then the program returns to line 50, the beginning of the System
Diagnostic Main Menu:

6100 CLOSE 2:GOTO 50

 Chapter 8
PoslOOJRepair Tes.
and .lIrn~ln
Chapters 2 through 8 have each covered individual components of the
Commodore system, examining and treating the problems that can occur within
a particular subsystem. This chapter looks at the Commodore system as a whole,
and provides a diagnostic module that exercises the entire system to check for
problems.
If something does go wrong with the computer and you repair it or take it
in for professional servicing, the first thing you want to do when it is returned
is check it out. This chapter describes and provides methods for testing the repaired
system to make sure everything works as it should .
When picking up the computer from servicing, treat it like an automobile
repair. If your car had been in for servicing with a mechanic, you wouldn't just
pay the bill and drive off. You would want to test drive it, or have the mechanic
show the work that had been done. If the car had a brake problem, you would
check to see that the brakes worked properly. If oil was leaking, you would see
that the leak was stopped. Only when satisfied that the problem was fixed would
you pay the bill and drive away.
Do the same when picking up the computer from servicing. Have the ser-
vice technician describe what was done, explain why it was done, and demonstrate
that the problem has been fixed. However, keep in mind that even whi Ie checking
the component at the repair shop, not all system functions can be checked. You'll
probably just see a few tests for the specific problem, demonstrating that the
particular component is working correctly.

152
 Commodore Care Manual 153

For example, if the system unit had a problem, you probably would have
just taken the system unit in for servicing, leaving the printer, disk drive, and
modem at home. But the computer is a system, consisting of a number of devices
and peripherals which all work together. Because of this, sometimes when there
is a problem in one device, it can manifest itself in another device. So even when
the technician demonstrates that the system unit is working fine, the complete
status is unknown until the unit is assembled at home with the entire system in
its usual configuration.
The diagnostic module covered in this chapter is a program that thoroughly
exercises the Commodore when it's new, when its configuration changes, or when
it returns from servicing. This Exerciser Module checks various components of
the Commodore system and leaves it running in a continuous mode so that it
can "burn in" for several hours, even overnight.
Burn-in thoroughly tests and exercises the system, and should be done for
12 to 24 hours. If there is a problem with the computer, it's better to discover
it during burn-in than while entering and processing valuable data. This is a good
practice widely used in industrial manufacturing and product testing.

FUNCTION OF THE EXERCISER

The System Exerciser Module calls on diagnostic tests that are already a part
of individual component diagnostic modules elsewhere in the System Diagnostic
Program. Specifically, it branches to routines in the Monitor Diagnostic Module,
Printer Diagnostic Module, and Disk Drive Diagnostic Module.
When the System Exerciser Module is accessed, a menu is displayed. This
menu prompts you to specify the devices to be tested, the monitor, printer, and/or
disk drives. You can specify any combination of devices to be included or excluded
from the Exerciser. These component parameters may be set up in whatever
combination is convenient and appropriate for the system.
Once the parameters are set up, the System Exerciser Module immediately
begins to perform the continuous test on the specified devices until you press
the RUN/STOP key. This means you could run the Exerciser for hours, even
overnight if desired.
If the monitor is to be tested, the Scroll Test, the Character Set Test, and the
Display Test are run. For more information on these tests, refer to Chapter 3.
If the printer is to be tested, the Sliding Alpha Test is run for ten lines, the
Echo Character Print Test is run on one line, and the Horizontal Tab Test and
Line Space Test are each run through once. For more information on these tests,
refer to Chapter 4.
If the disk drive is to be tested, the ReadIWrite Test is run, with records fi Iling
the disk and then being read back. The disk drives include some of the most
delicate components of the entire system, and should be tested after repair. For
more information on the ReadIWrite Test, refer to Chapter 6.
The System Exerciser begins with the monitor diagnostics, then goes to the
printer diagnostics, and finally the disk drives. When complete, the Exerciser cycles
back through to the monitor to start the process again. This cycle continues until
the RUN/STOP key is pressed to interrupt the Exerciser. Upon interruption, a
154 Post-Repair Test and Burn-In

message is displayed which indicates the number of cycles the Exerciser has run
through.
Because the Exerciser tests the three major components of the Commodore
system, the monitor, the disk drive(s), and the printer, it can indicate whether
there is a problem. If it's an obvious problem, it will probably surface immediately.
If there is a marginal or intermittent problem elsewhere in the system, it will show
up within a 24-hour burn-in run of the Exerciser.
The System Exerciser Module runs under BASIC, just like the rest of the System
Diagnostic Program. Because of this, the Exerciser is also testing an extensive
section of the system unit's machine instruction set.

RUNNING THE SYSTEM EXERCISER

When ready to run the Exerciser on the Commodore, make sure that the
components to be tested are ready for hours of testing. If the printer is part of
the test, make sure it is loaded with a sufficient quantity of continuous-form pa-
per. Check that there is enough ribbon to last throughout the duration of the printer
test. Blank, formatted diskettes should be in each of the drives being tested. Al-
though you might want to dim the monitor display, there is no danger from etching
(see Chapter 3 for more information about etching), because the display is
continually changing.
To run the System Exerciser, follow the instructions provided in "Running
the Diagnostic Program" in Chapter 1. Then, from the System Diagnostic Main
Menu, press E to initiate the Exerciser Module.
The screen clears and a prompt asks if you wish to test the monitor, yes or
no. Enter y or n, either upper- or lowercase, and press RETURN. A second prompt
asks if the printer is to be tested. Again, enter y or n.
A final prompt asks if the disk drive(s) are to be tested. Enter either y or n.
If the answer is yes, you are then prompted to enter the number of drives to be
exercised. All the disk drives on the Commodore can be tested through the
Exerciser. Enter 1, 2, 3 or 4. Then you are asked to enter the drive IDs for each
drive being tested. This ID is the disk drive number, such as 8 for the first drive,
9 for the second drive, or 10 for the third drive (Fig. 8-1).
Any combination of Exerciser parameters can be selected. Once these
parameters are all entered, the program begins exercising the system. If the mon-
itor is included in the Exerciser, the screen is filled with the results of the Display
Test. The screen then clears and runs through the Character Set Test. Finally the
Scroll Test is run for 50 repetitions.
If the printer is included in the Exerciser, it begins upon completion of the
monitor testing. Ten repetitions of the Sliding Alpha Test are printed. It then runs
through the Display Character Print Test and then prints a line of Es for the Echo
Character Print Test. The Horizontal Tab Test and finally the Line Space Test are
run, for a thorough printer test.
If the disk drive(s) is included in the Exerciser, it begins upon completion
of the printer testing. The Write/Read Test is run on each disk drive specified for
testing.
When this is completed, the program loops back and tests the monitor again,
 Commodore Care Manual 155

Exerciser Diagnostic

Test Monitor (Y or N)- y

Test Printer (Y or N)- y

Test Disk Drive(s) (Y or N)- y

How many drives to test- 1

Enter drive number for drive- 8

Enter drive type 1-1541 2-1571- 1

Fig. 8-1. Exerciser Module prompts.

then the printer, and so forth. The Exerciser runs in this continuous loop, running
the tests in a repeated cycle. To halt the Exerciser, press the RUN/STOP key. This
ends the System Exerciser Module, and also halts the entire System Diagnostic
Program.
To return to the Exerciser, enter GOTO 7430. The system returns to the system
Diagnostic Program at line 7430 in the code. This causes the message indicating
the number of passes the program has completed to be printed. You are then
prompted to enter any character to end the diagnostic. Once this is done, the
System Diagnostic Program returns to display the System Diagnostic Main Menu.
If the Exerciser is interrupted while it's running the disk drive test, you might
see a file called "TEST" show up in the diskette's directory. Delete this file from
the diskette. Normally, the diagnostic removes this file after it completes its run.
If one of the tests fail, the Exerciser halts. So if the printer runs out of paper,
or if something happens to the disk drive, the program stops at the point at which
the problem took place. An error message describing the problem is displayed,
so that you can take the appropriate action.

HOW THE SYSTEM EXERCISER MODULE WORKS

When the user chooses E from the System Diagnostic Main Menu, the program
branches to line 7200 for the beginning of the System Exerciser Module (Fig. 8-2).
Line 7200 begins by assigning variable EX equal to one. EX is the Exerciser
flag that is used in several modules throughout the diagnostic program. EX is
ordinarily equal to zero, allowing the monitor, printer, and disk drive diagnostic
156 Post-Repair Test and Burn-In

7200 EX=1:GOSUB 2990:REM "Exerciser Module"

7210 PRINT TAB(10)"Exerciser Diagnostic":PRINT
7220 INPUT "Test Monitor (Y or N)-";MN$:PRINT
7230 INPUT "Test Printer (Y or N)-";PT$:PRINT
7240 INPUT "Test Disle Drive(s) (Y or N)-";DD$
7250 IF DD$="N" OR DD$="n" THEN 7310
7260 PRINT:INPUT "How many drives to test-";DD
7265 DN="":DIM DN(DD) :DIM DTCDD)
7270 FOR 1=1 TO DO
7280 PRINT: INPUT "Enter drive m.mber for drive-";DN(I)
7290 PRINT:INPUT "Enter drive type 1-1541 2-1571-";DTCI)
7300 NEXT
7310 IF MN$="N" OR MN$="n" THEN 7330
7320 A$="X":A=50:GOSUB 1140
7340 IF PT$="N" OR PT$="n" THEN 7380
7350 OPEN 1,4,7
7360 A$="E":X=10:GOSUB 3650
7370 CLOSE 1
7380 IF DD$="N" OR DD$="n" THEN 7310
7390 FOR 1=1 TO DO
7395 GOSUB 2990
7400 D=DN(I):T=DT(I):GOSUB 5040
7410 NEXT
7420 PS=PS+1:GOTO 7310
7430 GOSUB 2990:CLOSE 1
7440 PRINT TAB(10)"Exerciser Diagnostic":PRINT
7450 PRINT TAB(3)"Total Passes through Exerciser-";PS
7460 GOSUB 3200
7470 EX=O:GOTO 50

Fig. 8-2. The System Exerciser Module listing.

modules to function in its usual standalone mode with user input. However, when
EX is set to 1, the program skips the various parts of the program which require
user intervention, such as entering a particular value.

7200 EX = 1:GOSUB 2990:REM "Exerciser Module"

The COSUB statement sends the program to the Clear Screen subroutine at line
2990. Finally, the REMARK statement indicates that this is the beginning of the
Exerciser module.
Line 7210 prints the title of the module on the screen:

7210 PRINT TAB(10)"Exerciser Diagnostic":PRINT

 Commodore Care Manual 157

Line 7220 prompts the user to indicate whether or not the monitor is to be tested.
The answer is placed into variable MN$:

7220 INPUT "Test Monitor (Y or N)·";MN$:PRINT

Line 7230 prompts the user to indicate whether or not the printer is to be tested.
The answer is placed into variable PT$:

7230 INPUT "Test Printer (Y or N)-";PT$:PRINT

Line 7240 prompts the user to indicate whether or not the disk drivels) are to
be tested. The answer is placed into variable DD$:

7240 INPUT "Test Disk Drive(s) (Y or N)-";DD$

Because the user's system can have more than one drive, and different types of
drives, further prompts are required regarding the disk drive test.
Line 7250 checks to see if the user has answered "no" to the Test Disk Drive(s)
prompt. If so, the program branches to line 7310, skipping the code asking for
further information about the disk drivels) to be tested:

7250 IF DD$="N" OR DD$="n" THEN 7310

If the user answered "yes" to the Test Disk Drive(s) prompt, the program falls
through to line 7260, which prompts the user for the number of drives to be tested.
The answer is placed into numeric variable DD:

7260 PRINT:INPUT "How many drives to test-";DD

Line 7265 sets dimension ON equal to null, in order to clear it. Disk number
variable DN is dimensioned by the disk quantity variable DD. Also, disk type
variable DT is dimensioned by the disk quantity variable DD. The variable DT
will indicate whether the disk type in question is a 1541 or 1571 disk drive:

7265 DN="":OIM ON(OD):OIM OT(DO)

Line 7270 is a FOR-TO loop, looping through the number of drives being
tested:

7270 FOR I = 1 TO 00

Line 7280 prompts the user for the drive number, and places the answer into
array DN(I). If the first drive is drive #8, for example, the first element of the array
becomes an 8:

7280 PRINT:INPUT "Enter drive number for drive-";ON(I)

158 Post-Repair Test and Burn-In

Line 7290 is a similar instruction. The user is prompted to enter the drive type:
1 signifies a 1541 drive, and 2 signifies a 1571 drive. The answer is placed into
array DT(I):

7290 PRINT:INPUT "Enter drive type 1-1541 2-1571-";OT(I)

Line 7300 is the NEXT statement that corresponds with the FOR-TO loop that
began in line 7270. This causes the code to loop as many times as there are drives
to test:

7300 NEXT

Line 7310 begins the actual system exercising. Here the program examines
which options the user has selected, then goes about executing them. This line
begins with an IF statement for the Monitor Diagnostic. If the user has chosen
not to exercise the monitor, the program branches to line 7330:

7310 IF MN$= "N" OR MN$= "n" THEN 7330

If the user did choose to exercise the monitor, the program falls through to line
7320, which sets variable A$ equal to X, which is used as the display character
in the monitor scroll test, and sets variable A equal to 50 for the number of
repetitions to scroll. Finally, GOSUB 1140 sends the program back to the
Monitor Diagnostic Module in order to perform the Scroll Test with these preset
parameters:

7320 A$= "X":A=50:GOSUB 1140

In the Monitor Diagnostic Module code, there are various checks to see wheth-
er or not EX is equal to one. If it is, the Exerciser is active, and the program jumps
past any lines that require user input. The Exerciser runs through the various tests
of the Monitor Diagnostic through to the Sprite Test. At that point, at line 1915,
there is a statement indicating that if the Exerciser is active, it should RETURN.
So when the program runs to that line, it returns back to line 7340.

Line 7340 then does the same check for variable PT$, the printer flag. If the
user has chosen not to test the printer, the program branches to line 7380:

7340 IF PT$="N" OR PT$="n" THEN 7380

If the user did choose to test the printer, the program falls through to line 7350,
which opens the printer as upper/lowercase device #1:

7350 OPEN 1,4,7

Line 7360 assigns variable A$ equal to E. This E is used as the character to

 Commodore Care Manual 159

be echoed in the Echo Character Print Test in the Printer Diagnostic. It also sets
X equal to ten for the number of lines to print in the Sliding Alpha test. Finally,
there is a GOSUB to line 3650, treating the entire Printer Diagnostic Module like
a large subroutine:

7360 A$= "E":X= 10:GOSUB 3650

Just as in exercising the monitor, there are checks for whether EX equals one
throughout the Printer Diagnostic code. When the Exerciser gets to line 4140,
it returns here to the Exerciser Module.
Line 7370 closes device #1, the printer:

7370 CLOSE 1

Line 7380 checks if the user opted to exercise the disk drivers). If not, the
program branches to line 7310:

7380 IF DO$="N" OR OO$="n" THEN 7310

If the user did choose to exercise the disk drivers), the program falls through to
line 7390, which is a FOR-TO loop. Variable DD holds the user input of the
number of drives to be tested, so this loops for the number of drives:

7390 FOR I = 1 TO DO

Line 7395 goes to the Clear Screen subroutine at line 2990, which clears the screen
of leftover messages and prompts from the previous test:

7395 GOSUB 2990

Line 7400 sets variable D, the disk number, equal to DN(I). DN is the array
in which the disk number is stored. I is an index. In the first pass through the
first disk, the program goes through DN(I). The second part of the statement sets
variable T, the disk type, equal to DT(I). Then the program goes back to line 5040
into the Disk Drive Diagnostic Module to run the write and read tests.

7400 0 = ON(I):T = DT(I):GOSUB 5040

When the Exerciser completes its run through the Disk Drive Diagnostic, it
returns to line 7410, the NEXT statement corresponding to the FOR-TO loop at
line 7390:

7410 NEXT

When all the specified disk drives have been tested, the program falls to line
7420. Line 7420 sets variable PS equal to PS + 1. When the user halts the program,
this variable indicates the number of passes the Exerciser has run, which is
especially useful if the Exerciser has been run for several hours or even overnight.
160 Post-Repair Test and Burn-In

The program then branches to line 7310, which returns the program to the process
loop at the beginning of the Exerciser module, with the prompts for which devices
to test:

7420 PS=PS+l:GOTO 7310

The Exerciser is an endless loop which the user can halt by pressing the
RUN/STOP key on the keyboard. When this is done, to continue with the rest of
the program, the user must enter the statement GOTO 7430.
Line 7430 is the last segment of the Exerciser Module. It branches to the Clear
Screen subroutine at line 2990, then closes device #1, in case the printer or disk
drive was left open at the time the program was halted:

7430 GOSUB 2990:CLOSE 1

Line 7440 prints the Exerciser Diagnostic title on the screen again:

7440 PRINT TAB(10)"Exerciser Diagnostic":PRINT

Line 7450 prints the total number of test passes on the screen, using variable PS
from line 7420, which has been counting the passes:

7450 PRINT TAB(3)"Total Passes through Exerciser-";PS

Line 7460 goes to the subroutine at line 3200, which prints the user prompt to
enter any character to end the test:

7460 GOSUB 3200

Line 7470 returns EX equal to zero again, to set the System Diagnostic Program
back to its usual mode of user-directed operation. The program then returns to
line 50, which is the beginning of the System Diagnostic Main Menu:

7470 EX=O:GOTO 50
 Chapter 9
Writing
Di_gn.stics
far OIlier
Peripherals
When there is a problem somewhere in the system, you want to be able to isolate
and identify its source. The System Diagnostic Program presented in this book
provides the means for doing this with the system unit, keyboard, monitor, print-
er, disk drives, and serial communication interface. You are able to perform the
necessary repairs on the indicated subsystem, based on this information.
However, if your system utilizes other peripherals not covered by this program,
it might be desirable to be able to write new diagnostic modules for them. In
this way, the System Diagnostic Program can grow with the computer system,
and new components will not be left out of the diagnostic loop that benefits the
rest of the system.
Using the joystick as an example, this chapter explains how to identify the
basic functions of a new device, and describes the types of problems you might
have with it. This chapter also tells how to find the information necessary for
developing the diagnostic that tests the device functions. Advice on flowcharting
and coding is provided, along with integration and testing procedures. This chapter
assumes that you are conversant in the BASIC programming language in which
the System Diagnostic Program is written .
If you are not currently familiar with BASIC but would like to be, obtain one
of the many excellent books on learning BASIC. There are also BASIC classes
available through computer stores, community colleges, and adult education
programs.

161
162 Writing Diagnostics for Other Peripherals

TYPES OF MICROCOMPUTER PERIPHERALS

There are many interesting peripheral devices available for the Commodore
systems. These peripherals include digitizer tablets, which let you draw and draft
with the computer. Voice recognition devices can recognize voice patterns and
even respond to verbal commands. Voice synthesizers can speak to you.
Other popular peripheral devices include the bar code reader, light pen,
mouse--even the video cassette recorder. The Commodore game paddles and
joysticks allow you to play various interactive games.
In addition to these peripherals, more and more devices are constantly being
invented, marketed, and made readily available to the Commodore computer user.

DEVELOPING A NEW DIAGNOSTIC MODULE

Begin considering the development of a new diagnostic module for the new
peripheral as soon as you have acquired some familiarity with it. When this new
device becomes an integral part of the permanent system, and not just a new
"toy," its own diagnostic should be developed.

Learn the Functions of the Device

The first thing to do when developing a new diagnostic module for a new
peripheral is to learn everything possible about how the device functions. Find
out specifically what the device is intended for and what it is designed to do.
Why did you buy it? What does it do? Experiment with the device. Explore its
possibilities. Try to do real work (or play) with it.

Read the Device Manual

Read the device documentation to learn about capabilities of which you may
not have been aware. Do this as soon as you obtain the new peripheral. The man-
ual typically includes two major sections: one covering actual operation of the
device, the other providing technical information that will prove useful in
developing and programming the diagnostic module. Never throwaway any
documentation that comes with a device.
The operation section of the manual describes functions and uses of the de-
vice, its special features, how to use it most efficiently, how to program it, and
how to integrate it with the other system components and software.
In addition to installation instructions, the technical section of the manual
describes various options and their settings. It also provides suggestions on setting
up your existing hardware and software in order for the new device to work prop-
erly and efficiently.
The manual usually also includes a troubleshooting guide which outlines prob-
lems that can occur and suggests remedial procedures to follow in response to
these problems. Examine the troubleshooting guide as a first step to developing
a new diagnostic module. It will make you familiar with typical problems for which
the diagnostic should test. The diagnostic must be developed before trouble
strikes-don't wait until there is a problem before looking at the troubleshooting
guide.
 Commodore Care Manual 163

The troubleshooting guide provides information about the particular device,

but does not take into account the software running with the device, the hardware
configuration of the system, or the type of interface. In other words, the
troubleshooting guide does not know your particular system, and therefore, cannot
specifically address your exact troubleshooting requirements. It would be
impossible for any troubleshooting guide to consider all these items, simply
because there are infinite possibilities and combinations.
Because of this, you can benefit from developing a customized troubleshooting
diagnostic for the device as it works with your particular system. The diagnostic
can then be integrated into the System Diagnostic Program as a new module.

DecIde What to Test For

Once you know the functions of the device, take the inverse of these functions
and test for them. In other words, if a device is supposed to perform a particular
function, you should test whether it does not perform this function.
Further research, either in the system technical manual, the device
documentation, or the BASIC programming manual, is necessary to find out how
to write programs that check for particular functions.

Create a Program Flowchart

Once you know the functions and problems for which to test, you can develop
the program flowchart. This flowchart becomes the program design and the "road
map" to writing the actual diagnostic code.
The flowchart outlines the various test routines that will exist within the
module, as well as any GOTO statements and FOR-TO loops. The flowchart can
also detail any new program functions and commands you have learned through
research on the particular device. Be as detailed as possible in the flowchart. This
makes subsequent coding much easier.
Flowcharting is the method by which the process or "flow" of a program
can be charted graphically. Arrows connect process and decision boxes,
representing the direction (or any change of direction) in which a program or
segment of a program will flow. Although there are a great number of flowcharting
symbols, only a small set of these is needed to accurately represent the program
flow.
Create the flowchart in two stages. In the first stage, express the fundamental
ideas of the program in plain English. Figure 9-1 is a flowchart for a simple segment
of a program aski ng users to enter thei r name, and then greeti ng them by name.
In the second stage, write a more detailed flowchart, translating the English
statements into BASIC commands. Now follow the arrows and add the line numbers
to the code to write the program as follows:

10 PRINT {CLR/HOME}
20 INPUT "Enter your name-";A$
30 PRINT "Hello ";A$
40 END
164 Writing Diagnostics for Other Peripherals

Fig. 9-1. A simple program flowchart.

Flowcharts can be detailed or brief according to personal preference_ If you're

a beginning or novice programmer, however, the more detailed the flowchart
is, the easier and more trouble-free the coding will tend to be. The objective is
to establish the program's flow and logic to the point where the program can easily
be written.

Write the Diagnostic Module

When the program flowchart is diagrammed, you're ready to begin actual
coding. When developing a new test, first make sure that all aspects of the system
are functioning properly. Do not develop a test on a malfunctioning system, or
with a peripheral that is experiencing a problem. If a test were developed on a
malfunctioning system, as soon as the problem were fixed, the results of the test
might well become null and void, and the test code itself could become obsolete.
When exploring new BASIC instructions for the new device, follow examples
presented in the BASIC manual, just to try them out. Educate yourself in this
manner, and get a good feel for what these instructions do before "hacking" the
System Diagnostic Program.
After creating a flowchart of your ideas and converting them to BASIC code,
write a stand alone version of the new diagnostic module and test it by itself before
integrating it with the System Diagnostic Program. Refer to the code of existing
 Commodore Care Manual 165

modules in Appendix A or Appendix B (depending on your system) to familiarize

yourself with the proper techniques.
Include the standard utility subroutines used throughout the System Diagnostic
Program to simplify and streamline the new code.

Integrate the New Module

When you insert the new module into the System Diagnostic Program, modify
lines 50 through 180 of the program where the Main Menu Module resides. Add
the module's title and identifier to the PRINT statement that I ists the menu options
on the screen. Also, insert the appropriate IF statement for the new module so
that the program branches to the proper line number where the new code begins.
Once this is done, add the code to the program. Have the I ine numbers of
the new code begin around 8000, or wherever the last diagnostic module stopped.

Test the New Diagnostic Module

Finally, test the diagnostic as an integrated module of the System Diagnostic
Program. Try out all the new tests with as many possibilities as you can imagine.
Try your best to find "bugs" and "break" the program. If and when you do find
bugs, fix the code where the problem occurred.
Also test the other modules of the System Diagnostic Program, to find out
if the new program is interacting with the original code in any adverse ways. This
testing process ensures accurate results when using the diagnostic in an actual
troubleshooting situation.

DEVELOPING THE JOYSTICK DIAGNOSTIC MODULE

Up to this point, development of a new diagnostic module has been treated
in generalized terms. To make the development process more clear, a concrete
example is provided in this section. This example uses the joystick as the new
peripheral for which a new diagnostic module will be developed.
Development of the Joystick Diagnostic Module is described, step-by-step.
This includes researching the functions of the joystick, writing the new code for
the Joystick Diagnostic, and testing the new module as integrated with the entire
System Diagnostic Program.
Between the general principles outlined in the previous section and the
concrete examples described in this section, you should gain a good understanding
of how a diagnostic module can be developed for any peripheral added to your
Commodore system.

Functions of the Joystick

The joystick is a pointing and "firing" device (Fig. 9-2). It is used to position
the cursor on the screen, typically in games. It is also used to "fire" a graphic
object, like a missile, at another graphic object, as part of the game. With the
joystick, you can "fly" a jet airplane, move a graphic robot, or control a laser
cannon.
166 Writing Diagnostics for Other Peripherals

Fig. 9-2. The Commodore joystick.

The joystick is a mechanical device with five internal switches. Four of these
switches control the four directional positions at which the joystick can point:
top, bottom, right, and left. The fifth switch controls the fire button at the top
of the joystick lever.
Two of the directional switches can be activated at one time. For example,
if the joystick is pointed diagonally toward the top right, both the top and right
joystick switches are activated. This means that there are eight different directional
positional positions that can be used, in addition to the fire button control.

Tracking a Graphic Object. The appropriate object on the screen moves in

accordance with the movement of the joystick. When the joystick is moved to
the right, the object on the screen tracks to the right. When the joystick is moved
to the left, the object tracks to the left. When the joystick is moved diagonally,
the object likewise tracks diagonally. The joystick causes the particular object
on the screen to follow its movements.

Pressing the FIRE Button. In addition to the pointing lever, the joystick
includes the FIRE button. The graphic object can be positioned at a certain location,
and then when the fire button is pressed, the computer is informed to take a certain
action as programmed. By clicking the button, the computer knows that something
is to be done with the item on the screen where the cursor is pointing. Typically,
this would be shooting something in a game.

Information about the Joystick

There are several sources that can provide the information necessary to write
programs for the joystick, particularly a diagnostic program for the joystick.
 Commodore Care Manual 167

The Commodore BASIC manual has a great deal of valuable information for
programming in Commodore BASIC. The joystick user's manual provides more
specific information. The amount of information included in the joystick manual
depends on the manufacturer. The manual will often include information on
installation and maintenance, uses and applications for the joystick, and perhaps
sample programs and a troubleshooting guide.
One of the best sources of information on programming the joystick, is the
Commodore Programmer's Reference Guide. In the 110 chapter, there is
information about programming the joystick. In addition, one of the appendices
includes documentation on the pinout configuration of the game port to which
the joystick is connected.
Find out all the possible positions in which a joystick can be placed. Find
out how the joystick button is activated. Find out new uses for the joystick of
which you might not have been aware. Any sample programs in the documentation
will provide a good idea of the proper approach and special commands for
developing a program for your own purposes.
Another very beneficial means for researching the joystick is an old defective
joystick. If there is a defective joystick available, or if yours goes bad and needs
to be replaced, experiment with the old one. It's already defective, so nothing
can be hurt by taking it apart and exploring the works. This will help you under-
stand the component better, which will later aid troubleshooting endeavors.

TROUBLESHOOTING AND REPAIR GUIDELINES

The joystick user's manual will usually provide information on maintenance,
troubleshooting, and possibly repair. This information, along with the following
possible problems, help you decide what kinds of diagnostic tests are needed
to troubleshoot these particular malfunctions.

Problem: Joystick Does Not Work At All

If the joystick does not work at all, there could be a problem with the interface
connection, with the joystick itself, or with the system unit. To isolate where the
problem lies, try the following solutions in the order given.

121 Solutions

D Make sure the joystick is firmly seated in its game paddle port (Fig 9-3). Unplug
it, and carefully plug it back in and see if it works.

D If it still does not work, unplug the joystick cable from its game paddle port,
and plug it into the second port. If the joystick works in the other game padd Ie
port, this indicates a problem in the original port in the system unit. Refer
to Chapter 2 for further instructions on troubleshooting the system unit.

LJ If the joystick does not work in either of the two game paddle ports, try
operating the joystick, along with the diagnostic program, on another system.
If the joystick works on the other system, this indicates a problem with your
system unit. Refer to Chapter 2 for system unit troubleshooting procedures.
168 Writing Diagnostics for Other Peripherals

game
port #1

Fig. 9-3. The joystick connected to game port #1.

o If the joystick does not work on the other system, this indicates a faulty joystick.
The easiest thing to do in this case is to simply replace it.

Problem: Joystick Does Not Work In a Particular Direction

The joystick has eight directional positions to which it can point: north, south,
east, west, northeast, northwest, southeast, and southwest. If the joystick does
not respond to one or more of these positions, this indicates a problem with the
internal direction switch.

[2J Solutions

o Check the cable connection and make sure the joystick connection is proper-
ly plugged in to the game paddle port.

o Following instructions found in the joystick user guide, carefully disassemble

the joystick. Spray contact cleaner onto the suspect switch. This should
" unstick" the switch .

o Swap another joystick onto your system, if available. If the other joystick works
on your system, then your joystick is defective, and should be replaced. If
the other joystick does not work on your system, this indicates a problem with
the system unit. Refer to Chapter 2 for further solutions.

Problem: Fire Button Does Not Work

The switch that controls the fire button can also get stuck.

121 Solutions

o Check the cable connection and make sure that the joystick connection is pro~
erly plugged in to the game paddle port.

o Following instructions found in the joystick user guide, carefully disassemble

the joystick. Spray contact cleaner onto the suspect switch. This should
"unstick" the switch.
 Commodore Care Manual 169

D Swap another joystick onto your system, if available. If the other joystick works
on your system, then your joystick is defective, and should be replaced. If
the other joystick does not work on your system, this indicates a problem with
your system unit. Refer to Chapter 2 for further solutions.

Joystick Tests
Once you have a fair understanding of the joystick, determine the kinds of
tests that would be most helpful in such a diagnostic module.

The Game Port Option. Because the Commodore includes two game paddle
ports, the diagnostic user instructions should include a prompt for which port
is to be tested. This will allow separate testing of both ports.

The Direction Test. The joystick is a series of switches which determine the
direction of movement or firing action of the object it is controlling. Because of
this, one particularly useful test would be an on-screen display tracking the
direction in which the joystick is pointing. This would let you diagnose whether
a particular switch or combination of switches is malfunctioning.
In such a direction test, when the joystick is in its neutral position, the screen
is clear. If the joystick is moved away from you, the word NORTH would appear
on the screen. Likewise, if the joystick is moved to your left, the word WEST
would appear on the screen. And if you were to move the joystick diagonally
to the lower right, the word SOUTHEAST would be displayed.
In order to develop such a directional test, determine how information is sent
from the joystick to the system unit, and how this information is accessed. This
is a relatively simple process. The joystick is connected to one of two game ports
located on the right side of the system unit (Fig. 9-3). One of the chips on the
system unit's motherboard is an input port, accepting and processing input from
these game ports.
When one of the joystick switches is activated, a particular memory location
is set in this input port chip. On the Commodore 64, this is memory location
56320 for the first port, and memory location 56321 for the second port. This
is a one-byte location which contains a numeric value. The following table
indicates the numeric value which corresponds to each joystick position:

neutral 0
up
down 2
left 4
up left diagonal 5
down left diagonal 6
right 8
up right diagonal 9
down right diagonal 10

The Joystick Diagnostic Module must include a tight loop that continuously
examines the appropriate game port memory location. As long as the value is
170 Writing Diagnostics for Other Peripherals

zero and the joystick is in the neutral position, the loop goes around continuously.
As soon as the user moves the joystick, the value changes, and the program can
go to a table that holds some comparison statements. If the value were one, the
program would display the word "NORTH" on the screen. If the value changed
to two, the program would display the word "SOUTH." This would let the user
make sure that the joystick's "sense of direction" is working properly.

The Fire Test. A second test necessary for joystick diagnostics involves the
fire button. When the fire button is pressed, a value of 15 is set into the game
port memory location. This can serve two purposes: to test the fire button, and
to quit from the joystick Diagnostic and return to the System Diagnostic Main
Menu.

The Joystick Module Flowchart

Once you have determined the functions to be tested as part of the Joystick
Diagnostic, and have worked out many of the testing details, the next step is to
develop the "road map" for writing the actual code. This road map is drawn in
the form of a program flowchart.
The program flowchart indicates the commands to be used when the code
for this program is actuaily being written. To help write the flowchart, and later
the actual code with all the attendant details, have the BASIC programming man-
ual nearby as a ready reference. The Commodore Programmer's Reference is also
an excellent resource. These books will help you research any specialized
instructions used to access commands for the joystick.
Once you are familiar with the special commands, instructions, formats, and
other idiosyncrasies about programming the joystick on the Commodore, the
module can be diagrammed in the flowchart. This flowchart reflects your research
about the joystick functions, and details the particulars of the two tests you've
decided to develop for this module. Figure 9-4 shows a possible flowchart for
the joystick Diagnostic Module.

Writing the Joystick Diagnostic Module

Once the flowchart is developed and diagrammed, the actual diagnostic code
can be written. Again, refer to the BASIC programming reference books. Also re-
fer to Appendix A if you have a Commodore 64, or Appendix B if you have a
Commodore 128, and see examples of how the other diagnostic modules have
performed certain activities. Go ahead and copy or refer to the simple routines,
such as the Clear Screen and Get-a-Key subroutines.

The Joystick Diagnostic Module Listing. Based on the flowchart, the program
code might look similar (although it could have very many variations) to the listing
as shown in Fig. 9-5.

How the Joystick Diagnostic Module Works. just as was done with the oth-
er modules within the System Diagnostic Program, the first things to be done in
this module are to clear the screen, position the cursor, provide an identifying
 Commodore Care Manual 171

Examine
Joystick
Port

Find
Direction
In Array

Set to
Port 1

Set to
Port 2

Fig. 9-4. The Joystick Diagnostic Module program flowchart

REMARK statement, and print the module's title on the screen. This begins at line
7000, which clears the screen, positions the cursor, and identifies the module:

7000 D$="":DIM D$(10):GOSUB 2990

REM" Joystick Module"

Line 7002 begins a FOR-NEXT loop which initializes an array:

172 Writing Diagnostics for Other Peripherals

7000 D$="":DIM D$(10):GOSUB 2990:

REM "Joystick Module"
7002 FOR 1=1 TO 10
7004 READ D$(I):NEXT
7006 DATA "NORTH","SOUTH",'II',"IJEST"
7007 DATA "NORTHIJEST","SOUTHIJEST"
7008 DATA "","EAST","NORTHEAST","SOUTHEAST"
7010 PRINT TAB(10) "Joystick Diagnostic":PRINT
7020 PRINT TABU) "lJhich Port to Test 1 or 2-";P
7030 IF P<>2 THEN P=1
7040 PRINT:PRINT "Press Fire Button to End Test"
7050 IF P=1 THEN J=56320
7055 IF P=2 THEN J=56321
7060 VL=PEEK(J)
7070 FB=VL AND 16
7080 JD=15-(VL AND 15)
7090 IF FB=16 THEN 7110:REM Fire button was pressed
7100 GOTO 50
7110 IF JD=O THEN 7060
7120 PRINT D$(JD)
7130 GOTO 7060

Fig. 9-5. The Joystick Diagnostic Module listing.

7002 FOR 1=1 TO 10

Line 7004 reads variable D$, which is indexed by I. I is set from one to ten,
meaning there are ten pieces of data loaded into the array. The data for the array
follow in lines 7006, 7007, and 7008:

7004 READ D$(I):NEXT

7006 DATA "NORTH","SOUTH","","WEST"
7007 DATA "NORTHWEST","SOUTHWEST"
7008 DATA "","EAST","NORTHEAST","SOUTHEAST"

These data specify the position indicators that are to be printed on the screen
depending on the direction in which the joystick is moved. These data are placed
in the array according to the possible values that can be returned when the program
PEEKs into the memory location variable where the joystick input information
resides.

e128 USERS: Lines 7002 through 7009 are modified in the e128 code to
reflect the different switch positions of the directions in the array.

Line 7010 prints the name of the Joystick Diagnostic at the top of the screen:
 Commodore Care Manual 173

7010 PRINT TA8(10) "Joystick Diagnostic":PRINT

Line 7020 prompts the user to select the game port to be tested, port 1 or port
2. The value entered is placed into variable P:

7020 PRINT TAB(7) "Which Port to Test 1 or 2-";P

Line 7030 fixes the program so that if the value entered is anything but a two,
P is automatically set to one. This ensures that only the values one or two are
ever placed into variable P:

7030 IF P< >2 THEN P=1

Line 7040 prints a message that instructs the user to end the test by pressing
the FIRE button on the joystick:

7040 PRINT:PRINT "Press Fire Button to End Test"

Line 7050 checks to see if P is equal to one. If it is, then variable J is set equal
to 56320, which is the memory location that holds the input information for game
port #1. If P is equal to two, then J is set to 56321, which is the memory location
that holds the input information for game port #2:

7050 IF P=1 THEN J=56320

7055IFP=2THENJ=56321

Line 7060 sets variable VL equal to the contents of location L which is set
up either for game port #1 or game port #2:

7060 VL = PEEK(J)

e128 USERS: Lines 7050 through 7060 are modified to reflect the use of
the e128 joystick JOY command.

Line 7070 sets variable FB equal to variable VL, which is derived from the
PEEK statement, after going through the logical AND of 16 in the array. This
instruction filters out some unnecessary data that it picked up from the PEEK
operation. All that is necessary for the purposes of this program is that the input
value equal a number between zero and 16:

7070 FB=VL AND 16

Line 7080 sets variable JD equal to 15 minus VL after it went through the
logical AND statement. This again filters out extra data, and will also help check
when the FIRE button is depressed on the joystick:
174 Writing Diagnostics for Other Peripherals

7080 JD= 15-(VL AND 15)

Line 7090 checks to see if variable FB is equal to 16:

7090 IF FB=16 THEN 7110:REM Fire button was pressed

If it is, the program branches to line 7110. If it is not equal to 16, the program
falls through to line 7100, which loops back to line 50, the beginning of the System
Diagnostic Main Menu:

7100 GOTO 50

If FB is not equal to 16, the FIRE button was not pressed, and the program
branches to line 7110. Line 7110 checks whether variable JD (joystick direction)
is equal to zero. If it is, the joystick is in the neutral position, so the program returns
to line 7060:

7110 IF JD=O THEN 7060

If JD is not equal to zero, the program falls through to line 7120, wh ich pri nts
the contents of variable D$. D$ is the array set up at the beginning of the module,
indexed by variable )D. Therefore, if JD contains a value of one, for example,
then the word NORTH is printed on the screen, indicating that the user is pointing
the joystick forward.

7120 PRINT D$(JD)

The program then falls through to line 7130, which immediately sends the
program back to line 7060 for the loop looking for another value again. In this
manner, the user can continue to check the various joystick directions.

7130 GOTO 7060

When the user wants to end the diagnostic, the FIRE button can be tested at
the same time. If the FIRE button does not cause the program to exit to the System
Diagnostic Main Menu, there is probably a problem with the button. Press the
RUN/STOP key to end execution of the entire program, then refer to the
"Troubleshooting and Repair Guidelines" earlier in this chapter to continue with
diagnostic and repair efforts.
If the FIRE button is working correctly, the program branches all the way back
to line 50 for the beginning of the System Diagnostic Main Menu, at which point
the user can choose another diagnostic module or quit the program.

Integrating the Module with the System Diagnostic Program

Once the code is written for the Joystick Diagnostic Module, you must
integrate it with the rest of the System Diagnostic Program.
 Commodore Care Manual 175

First, modify the System Diagnostic Main Menu routine, which displays and
accesses all the diagnostic module options. Look at lines 50 through 90 of the
program where the Main Menu Module resides. Add the joystick Diagnostic
identifier to the PRINT statement that lists the menu options on the screen. Also,
insert the appropriate IF statement for the joystick Diagnostic identifier in lines
110-170, so that the program branches to the beginning of the joystick Diagnostic
Module when the appropriate key, perhaps a j, is pressed.
Once this is done, add the code to the program. A good place to append
the new code is starting at line 7000, as was done in this chapter's example. This
begins the new module where the last diagnostic module stopped.

Testing the Joystick Diagnostic Module

The last thing left to do is to test the joystick Diagnostic as it now resides
as an integrated module of the System Diagnostic Program. Try out the tests in
all the different directions. Try to "break" the program, and if you do, find and
fix the code where the problem occurred.
Once you have completed these research, flowcharting, coding, integration,
and testing procedures, the joystick Diagnostic Module is ready for real work when-
ever troubleshooting and diagnostics are needed.
 Appendix A

Co• •adora 64
Iysta.
Dlagnaslic
iProgra_ Llsll••
REM "COfTJ1lOdore 64"
5 REM "System Diagnostic Program Copyright 1988
TAB BOOKS Inc."
10 POKE 53272,23:DIM K$(63):REM Set Character Set
20 DATA "INST/DEL","RETURN","CRSR RTOI,OIF7",OIF1","F3","F6",
"CRSR UP", 0I 3","II","A"
21 DATA "4","Z","S",I'E"," 1I,1I5",lIr","O","6","CII,IIF",
"TII, "X", 117 11 , IIY","G", 118", 118"
22 DATA IIH","U",IIV","9 11 ,III",IIJ","O","MII,IIK",IIOII,"N",
"+", lip", ilL 11,11_11,11.11,11: II,"@II
23 DATA II,","£II,"*",";II,"CLR/HOMEII,II 1I,1I=",lItll,II/II,"1I1,
"-"," ","2","SPACE"
24 DATA" ","Q"
25 FOR 1=0 TO 62: READ K$(I):NEXT
30 DIM R(8):DATA 1,2,4,8,16,32,64,128
35 FOR 1=0 TO 7:READ R(I):NEXT
50 GOSUB 2990: PRINT TAB(12) "System Diagnostic":PRINT:
60 PRINT TAB(3) "<K>eyboard Text <S>erial Comm Test"
70 PRINT TAB(3) "<M>onitor Test <D>isk Drive Test":
80 PRINT TAB(3) "<C>assette Test <J>oystick Test":
85 PRINT TAB(3) "<P>rinter Test <E>xerciser":
90 PRINT TAB(16) "<Q>uit":PRINT:PRINT TAB(12)
"Enter Selection"

176
 Commodore 64 System Diagnostic Program Listing 177

100 GOSUB 3000:REM Get Key Command

110 IF AS="K" OR AS="k" THEN 200
120 IF AS="M" OR AS="m" THEN 800
130 IF AS="P" OR AS="p" THEN 3500
135 IF AS="C" or AS="c" THEN 4200
140 IF AS="D" OR AS="d" THEN 5000
150 IF AS="S" OR AS="s" THEN 6000
160 IF AS="E" OR AS="e" THEN 7200
165 IF AS="J" OR AS="j" THEN 7000
170 IF AS="Q" OR AS="q" THEN END
180 GOSUB 3100:GOTO 80
200 REM"Keyboard Diagnostic Module"
210 POKE 53272,23:S1=1:GOSUB 630
220 AS="":KYS="":GOSUB 3000
230 N=ASC(AS)
260 IF ASC(AS)=19 THEN GOTO 740
270 IF ASC(AS)=5 THEN KYS="ctrl 2:GOTO 600
280 IF ASC(AS)=17 THEN AS=" ":KYS="crsr down":GOTO 600
290 IF ASC(AS)=18 THEN KYS="rvs on":GOTO 600
300 IF ASC(AS)=20 THEN AS=" ":KYS="inst del":GOTO 600
310 IF ASC(AS)=28 THEN KYS="ctrl 3":GOTO 600
320 IF ASC(AS)=29 THEN AS=" ":KYS="cursor right":GOTO 600
330 IF ASC(AS)=30 THEN KYS="ctrl 6":GOTO 600
340 IF ASC(AS)=31 THEN KYS="ctrl 7":GOTO 600
350 IF ASC(AS)=141 THEN KYS="shift return":GOTO 600
360 IF ASC(AS)=142 THEN KYS="upper case":GOTO 600
370 IF ASC(AS)=144 THEN KYS="ctrl 1":GOTO 600
380 IF ASC(AS)=145 THEN KYS=" ":KYS="cursor up":GOTO 600
390 IF ASC(AS)=146 THEN KYS="rvs off":GOTO 600
400 IF ASC(AS)=147 THEN GOTO 740
410 IF ASC(AS)=148 THEN AS=" ":KYS="inst del":GOTO 600
420 IF ASC(AS)=156 THEN KYS="ctrl 5":GOTO 600
430 IF ASC(AS)=157 THEN AS=" ":KYS="cursor left":GOTO 600
440 IF ASC(AS)=158 THEN KYS="cntrl 8":GOTO 600
450 IF ASC(AS)=159 THEN KYS="ctrl 4":GOTO 600
460 IF ASC(AS)=133 THEN KYS="f1":GOTO 600
470 IF ASC(AS)=134 THEN KYS="f3" :GOTO 600
480 IF ASC(AS)=135 THEN KYS="f5":GOTO 600
490 IF ASC(AS)=136 THEN KYS="f7":GOTO 600
500 IF ASC(AS)=137 THEN KYS="f2":GOTO 600
510 IF ASC(AS)=138 THEN KYS="f4":GOTO 600
520 IF ASC(AS)=139 THEN KYS="f6":GOTO 600
530 IF A5C(AS)=140 THEN KYS="f8":GOTO 600
560 IF 5=0 OR S=1 THEN 600
570 IF S=2 THEN KYS="C= ":GOTO 595
580 IF S<>4 THEN GOTO 710
590 KY$="CTRL "
178 Commodore Care Manual

595 KYS=KYS+KS(K)
600 GOSUB 630
610 PRINT TAB(5) ASiTAB(13) NiTAB(23) KYSiTAB(35) S1
620 GOTO 220
630 GOSUB 2990
640 V=PEEK(53272)
650 IF V=21 THEN S1=1:GOTO 680
660 S1=2:PRINT TABU) "Keyboard Diagnostic Module":PRINT
670 PRINT TAB(2) "Character Value Key Combination Set":GOTO 700
680 PRINT TAB(7) "keyboard diagnostic roodule":PRINT
690 PRINT TAB(2) "character value key combination set"
700 PRINT TAB(2)"--------- ----- --------------- ---":RETURN
710 GOSUB 630
720 PRINT "An illegal shift code was encountered!"
730 PRINT "your keyboard needs service": GOTO 220
740 POKE 53272,23:PRINT "{BLUE}":GOTO 50

BOO GOSUB 299O:REM "Monitor Diagnostic Module"

810 PRINT TAB(6) "Monitor Diagnostic":PRINT
820 PRINT TAB(5) "1 ••• Display Test":PRINT
830 PRINT TAB(5) "2 ••• Al ignnent Test":PRINT
840 PRINT TAB(5) "3 .•• Character Set Test":PRINT
850 PRINT TAB(5) "4 .•. Color Test":PRINT
860 PRINT TAB(S) "5 .•• Scroll Test":PRINT
870 PRINT TAB(S) "6 .•• Sprite Test":PRINT
890 PRINT TAB(S) "Press CLR/HOME to End Diagnostic"
900 GOSUB 3000
1000 IF ASC(AS)=19 THEN 50
1010 IF AS="1" THEN 1090
1020 IF AS="2" THEN 1180
1030 IF AS="3" THEN 1320
1040 IF AS="4" THEN 1440
1050 IF AS="5" THEN 1650
1070 IF AS="6" THEN 1770
1080 GOSUB 3100:GOTO 900
1090 GOSUB 299O:REM Display Character Set Test
1100 PRINT TAB(14) "Display Test":PRINT
1110 PRINT "Enter Any Character to Fill Screen":PRINT
1120 PRINT "Press CLR/HClolE to End Test"
1130 GOSUB 3000
1132 PRINT "{CLR/HOME}"
1135 IF ASC(AS)=19 THEN 800
1140 FOR 1=1 TO 999
1150 PRINT ASi:NEXT
1155 IF EX=1 THEN 1360
1160 GOTO 1130
1180 GOSUB 299O:REM Alignment Test
 Commodore 64 System Diagnostic Program Listing 179

1185 POKE 53272,21

1190 PRINT TAB(H) "alignnent test":
1200 PRINT CHRS(176)i:FOR 1=1 TO 18: PRINT CHRS(99);:NEXT
1210 PRINT CHRS(178);:FOR 1=1 TO 18: PRINT CHRS(99);:NEXT
1220 PRINT CHRS(174):
1230 FOR 1=1 TO 10: PRINT CHRS(98);TAB(19)CHRS(98);
TAB(38)CHRS(98):NEXT I
1240 PRINT CHRS(171);:FOR 1=1 TO 18 PRINT CHRS(99);:NEXT
1250 PRINT CHRS(123);:FOR 1=1 TO 18 PRINT CHRS(99);:NEXT
1260 PRINT CHRS(179)
1270 FOR 1=1 TO 10:PRINT CHRS(98);TAB(19) CHRS(98);TAB(38)
CHRS(98):NEXT
1280 PRINT CHRS(173);:FOR 1=1 TO 18:PRINT CHRS(99);:NEXT
1290 PRINT CHRS(177);:FOR 1=1 TO 18:PRINT CHRS(99);:NEXT
1300 PRINT CHRS(189):GOSUB 3200
'1310 POKE 53272,23:GOTO 800
1320 GOSUB 2990:REM "Character Set Test"
1330 PRINT TAB(11) "Character Set Test"
1340 PRINT:PRINT "Enter Character Set (1) or (2)-"
1350 GOSUB 3000
1360 IF AS="1" THEN POKE 53272,21
1370 FOR 1=32 TO 255
1380 IF 1=128 OR 1=130 OR 1=131 OR 1=132 OR 1=141
1=143 OR 1=144 THEN 1410
1390 IF 1=145 OR 1=146 OR 1=147 OR 1=148 OR 1=156
OR 1=157 OR 1=158 THEN 1410
1395 IF 1=159 THEN 1410
1400 PRINT CHRS(I);+" ";
1410 NEXT
1415 IF EX=1 THEN POKE 53272,23:GOTO 1440
1420 PRINT:GOSUB 3200
1430 POKE 53272,23:GOTO 800
1440 GOSUB 2990:REM "Color Test"
1450 PRINT TAB(15) "Color Test":PRINT
1460 "CS="XXXXXXXXXXXXXXXXXXXX"
1470 PRINT "{CTRL 1} Black";TAB(12) CS
1480 PRINT "(CTRL 2) lIhite";TAB(12) CS
1490 PRINT "(CTRL 3) Red";TAB(12) CS
1500 PRINT "(CTRL 4) Cyan";TAB(12) CS
1510 PRINT "(CTRL 5) Purple";TAB(12) CS
1520 PRINT "(CTRL 6) Green"iTAB(12) CS
1530 PRINT "(CTRL 7) Blue"iTAB(12) CS
1540 PRINT "(CTRL 8) Yellow";TAB(12) CS
1550 PRINT "{C= 1} Orange";TAB(12) CS
1560 PRINT "(C= 2) Brown";TAB(12) CS
1570 PRINT "(C= 3) Lt. Red";TAB(12) CS
1580 PRINT "(C= 4) Gray 1";TAB(12) CS
180 Commodore Care Manual

1590 PRINT "{C= 5} Gray 2";TAB(12) C$

1600 PRINT "(C= 6) Lt. Green";TAB(12) C$
1610 PRINT "{C= 7} Lt. Blue";TAB(12) C$
1620 PRINT "(C= 8) Gray 3";TAB(12) C$
1625 IF EX=l THEN PRINT "{C= 7}":GOTO 1680
1630 PRINT:GOSUB 3200
1640 PRINT "(C= 7}":GOTO BOO
1650 GOSUB 2990:REM "Scroll Test"
1660 PRINT TAB(15) "Scroll Test":PRINT
1670 PRINT "Enter the NlSIlber of Repetitions-";A:PRINT
1680 N=31
1690 FOR 1=1 TO A
1700 N=N+l:IF N>71 THEN N=32
1710 FOR X=l TO 40
1720 PRINT CHR$(N);:N=N+1
1730 IF N>71 THEN N=32
1740 NEXT X
1750 NEXT I
1755 PRINT
1757 IF EX=l THEN 1770
1760 GOSUB 3200
1765 GOTO 800
1770 GOSUB 2990:REM "Sprite Test"
1780 PRINT TAB(15)"Sprite Test"
1790 FOR S=2040 TO 2047:POKE S,13:NEXT
1792 FOR S=832 TO 894:POKE S,255:NEXT
1BOO V=53248:POKE V+21,255
1810 FOR S=39 TO 46:POKE V+S, l:NEXT S
1815 R=O
1820 FOR 1=0 TO 7
1830 POKE 53269,PEEK(53269)OR(211)
1840 FOR X=24 TO 255
1850 POKE (V+I*2),X:POKE (V+I*2+1),152
1860 NEXT X
1870 POKE (V+16),R(I)
1880 FOR X=O TO 65
1890 POKE (V+(1*2»,X:POKE (V+(1*2+1»,152
1895 NEXT X
1897 POKE V+16,PEEK(V+16)AND 254
1900 POKE 53269,PEEK(53269)AND(255-211)
1910 NEXT I
1915 IF EX=l THEN RETURN
1920 PRINT:GOSUB 3200
1930 GOTO 800

2900 PRINT "{HOME/CLEAR)":RETURN:REM "Clear Screen Routine"

3000 GET A$:IF A$="" THEN 3000:REM "Get a Key Routine"
 Commodore 64 System Diagnostic Program Listing 181

3005 K=PEEK(197):S=PEEK(653)
3010 RETURN
3099 REM "Beep Routine"
3100 FOR L=54272 TO 54296:POKE L,O:NEXT
3110 POKE 54296,15:POKE 54277,90:POKE 54278,1:
POKE 54273,21:POKE 54272,31
3120 POKE 54276,33
3130 FOR T=1 TO 50:NEXT
3140 POKE 54276, 16:RETURN
3200 PRINT TAB(7)"press any key to end test";
3210 GOSUB 3000
3220 RETURN
3300 PRINT TAB(7)"press any key to continue":RETURN

3500 REM "Printer Diagnostic Module"

3510 GOSUB 2900:PRINT TAB(11) "Pr.inter Diagnostic":PRINT
3515 PRINT TAB(3)"1 ••• Sliding Alpha Test":PRINT
3517 PRINT TAB(3)"2 .•• Display Character Print Test":PRINT
3518 PRINT TAB(3)"3 ... Echo Character Print Test":PRINT
3519 PRINT TAB(3)"4 ... Horizontal Tab Test":PRINT
3520 PRINT TAB(3)"5 ..• Line Feed Test":PRINT
3530 PRINT TAB(5)"Press CLR/H()I1E to End Diagnostic
3535 OPEN 1,4,7:REM "Open as Upper/Lower case"
3540 GOSUB 3000:IF ASC(A$)<>19 THEN 3560
3550 CLOSE 1:GOTO 50
3560 IF A$="1" THEN 3630
3570 IF A$="2" THEN 3750
3580 IF A$="3" THEN 3920
3590 IF A$="4" THEN 4010
3600 IF A$="5" THEN 4070
3610 GOSUB 3100:GOTO 3540
3630 REM "Sl iding Alpha Test"
3640 GOSUB 2990:PRI NT TAB( 11) "Sl iding Alpha Test": PR I NT
3645 INPUT "Enter the nllT1ber of repetitions-";X
3650 N=31
3660 FOR 1=1 TO X
3670 LS="":N=N+1:IF N>111 THEN N=32
3680 FOR A=1 TO 80
3690 L$=L$+CHR$(N):N=N+1
3700 IF N>111 THEN N=32
3710 NEXT A
3720 PRINT#1,L$;:NEXT I
3730 IF EX=1 THEN GOTO 3760
3735 CLOSE 1
3740 GOTO 3500
3750 REM Display Character Print Test
3760 GOSUB 2990:PRINT TAB(6)"Display Character Print
182 Commodore Care Manual

Test":L$="":N=1
3770 CLOSE 1
3780 OPEN 1,4:REM "Open as Upper Case Only
3790 FOR 1=32 TO 255
3800 IF N=80 THEN PRINT#1,L$;:N=1:L$="":GOTO 3820
3810 L$=L$+CHRS{l )+" ":N=N+1
3820 NEXT I
3830 CLOSE 1
3840 OPEN 1,4, 7:REM "Open as Upper/Lower Case"
3850 FOR 1=32 TO 255
3860 IF N=80 THEN PRINT#1,LS;:N=1:L$="":GOTO 3880
3870 LS=LS+CHRS(I)+" ":N=N+1
3880 NEXT I
3890 IF LS<>"" THEN PRINT#1,L$
3900 IF EX=1 THEN GOTO 3950
3905 CLOSE 1
3910 GOTO 3500
3915 REM "Echo Character Print Test"
3920 GOSUB 2990:PRINT TAB(7)"Echo Character Print Test":
PRINT
3925 PRINT TAB(5)"Enter the Character to Ecno":PRINT
3935 PRINT "Press the CLR/HC»4E Key to End the Test"
3940 GOSU~ 3000:IF ASC(AS)=19 THEN CLOSE 1:GOTO 3500

3950 LS=""
3970 FOR 1=1 TO 80
3980 L$=L$+A$:NEXT
3990 PRINT#1,L$
4000 GOTO 3940
4010 REM Horizontal Tab Test
4020 GOSUB 2990:PRINT TAB(10)"Horizontal Tab Test"
4030 FOR 1=1 TO 80
4040 PRINT #1,TAB(I)"*":NEXT
4050 IF EX=1 THEN GOTO 4080
4060 CLOSE 1:GOTO 3500
4070 REM "Line Feed Test"
4080 GOSUB 2990:PRINT TAB(13)"Line Feed Test"
4100 FOR 1=2 TO 10
4110 FOR A=1 TO I
4115 PRINT#1,"":NEXT A
4120 N$=STR$(1-1)
4130 PRINT#1,"There have been ";NS;" line feeds"; :NEXT I
4140 IF EX=1 THEN RETURN
4150 CLOSE 1:GOTO 3500

4200 REM "Cassette Diagnostic Module"

4210 GOSUB 2900
4220 PRINT TAB(10) "Cassette Diagnostic":PRINT
 Commodore Care Manual 183

4230 PRINT TAB(10) "1. .. IJrite/Read Test":PRINT

4240 PRINT TAB(10) "2 ... Read Only Test":PRINT
4250 PR I NT TAB( 10) "Enter Coomand"
4260 GOSUB 3000
4270 IF A$="l" THEN 4310
4280 IF A$="2" THEN 4420
4290 GOSUB 3100
4300 GOTO 4260
4310 GOSUB 299O:PRINT TAB(13)"IJrite/Read Test":PRINT
4320 PRINT "Place a blank tape in the cassette drive"
4330 PRINT "and press RECORD.":PRINT
4340 GOSUB 3300:GOSUB 3000:PRINT
4350 OPEN 1,',1, "Test-Tape 1"
4360 FOR 1=1 TO 100
4370 PRINT#1,CHR$(170):NEXT
4380 CLOSE l:OPEN 1,1, 1,"Test-Tape 2"
4390 FOR 1=1 TO 100
4400 PRINT#l CHR$(85):NEXT
4405 CLOSE ,
4410 PRINT:PRINT "Rewind the tape and press PLAY"
PRINT:GOSUB 3200
44'5 GOTO 4460
4420 GOSUB 2990
4430 PRINT TAB(13) "Read Only Test":PRINT
4440 PRINT "Place the test tape in the cassette drive"
4450 PRINT "and press PLAY"
4455 PRINT:GOSUB 3300:GOSUB 3000:PRINT
4460 OPEN 1,',O,"Test-Tape 1"
4470 FOR 1=1 TO 100
4480 INPUT#l,AS
4490 IF A$<>CHR$(170) THEN E=E+l
4495 NEXT
4500 CLOSE 1
4510 OPEN l,',O,"Test-Tape 2"
4520 FOR 1=1 TO '00
4530 INPUT#' ,AS
4540 IF AS<>CHRS(85) THEN El=E'+1
4550 NEXT I
4560 CLOSE 1:PRINT
4570 PRINT TAB(3) "There were ";E;" High Value errors"
:PRINT
4580 PRINT TAB(3) "There were ";El;" Low Value errors"
:PRINT
4590 GOSUB 3200
4600 GOTO 50
184 Commodore 64 System Diagnostic Program Listing

5000 REM: "Disk: Drive Diagnostic ModuLe"

5010 FOR 1=1 TO 8:HV$=HV$+CHR$(170):NEXT
5020 LV$="":FOR 1=1 TO 8: LV$=LV$+CHR$(85):NEXT
5030 GOSUB 2990:PRINT TAB(10)"Disk: Drive Diagnostic":PRINT
5035 INPUT "Which Drive Do You Want To Test-";D:PRINT
5036 IF 0<8 OR 0>15 THEN PRINT "InvaLid Disk Nurreer":
GOTO 5035
5037 INPUT "Enter Drive Type 1-1541 2-1571";T
5038 IF T<>2 THEN T=l
5040 BF$=HV$:NM$="High VaLues"
5050 FOR 1=1 TO 2
5060 OPEN 1,D,2,"TEST,s,w"
5070 PRINT:PRINT"Writing ";NM$;" to Disk"
5072 IF T=2 THEN Z=33600
5074 IF T=l THEN Z=16800
5075 FOR A=l TO Z
5077 Bl$=""
5080 PRINT#l,BF$
5090 NEXT A
5095 CLOSE 1
5100 OPEN 1,0,2, "TEST,s,r"
5110 PRINT "Reading ";NM$;" from Disk":PRINT
5115 FOR A=l TO Z
5120 INPUT#l,B$
5140 IF B$<>BF$ THEN PRINT "Error Reading ";NM$:E=E+l
5150 NEXT
5160 CLOSE 1
5165 OPEN 15,8,15,"sO:TEST":CLOSE 15
5170 BF$=LV$:NM$="Low VaLues":NEXT I
5180 PRINT:PRINT "There were ";E;" errors encountered"
5182 OPEN 15,8, 15:INPUT#15,DS,DS$,T,S:PRINT:PRINT DS;
",",DS$+",";T;",";S:PRINT
5183 CLOSE 15
5185 IF EX=l THEN RETURN
5190 GOSUB 3200
5200 GOTO 50

6000 GOSUB 2990:REM "SeriaL COITITl ModuLe"

6010 PRINT TAB(3) "Serial Cormunications Diagnostic":
PRINT
6020 PRINT TAB(7)"Press CLR/Ha-IE to End Test":PRINT
6025 GOSUB 3300
6030 r.oSUB 3000: GOSUB 2990
6040 OPEN 2,2,3,CHR$(6)+CHR$(0)
6050 GET #2,A$
6060 IF A$="" THEN 6070
6065 PRINT A$:
 Commodore Care Manual 185

6070 GET A$:IF A$="{CLR/HCJoIE}" THEN 6100

6075 IF A$="" THEN 6050
6080 PRINT#2,A$;:GOTO 6050
6100 CLOSE 2:GOTO 50

7000 D$="":DIM D$(10):GOSUB 2990:

REM "Joystick Module"
7002 FOR 1=1 TO 10
7004 READ D$(I):NEXT
7006 DATA "NORTH","SOUTH",'"',"IIEST"
7007 DATA "NORTHIIEST","SOUTHIIEST"
7008 DATA "","EAST","NORTHEAST","SOUTHEAST"
7010 PRINT TAB(10) "Joystick Diagnostic":PRINT
7020 PRINT TAB(7) "lIhich Port to Test 1 or 2-";P
7030 IF P<>2 THEN P=1
7040 PRINT:PRINT "Press Fire Button to End Test"
7050 IF P=1 THEN J=56320
7055 IF P=2 THEN J=56321
7060 VL=PEEK(J)
7070 FB=VL AND 16
7080 JD=15-(VL AND 15)
7090 IF FB=16 THEN 7110:REM Fire button was pressed
7100 GOTO 50
7110 IF JD=O THEN 7060
7120 PRINT D$(JD)
7130 GOTO 7060

7200 EX=1 : GOSUB 2990:REM "Exerciser Module"

7210 PRINT TAB(10)"Exerciser Diagnostic":PRINT
7220 INPUT "Test Monitor (Y or N)-";MN$:PRINT
7230 INPUT "Test Printer (Y or N)-";PT$:PRINT
7240 INPUT "Test Disk Drive(s) (Y or N)-";DD$
7250 IF DD$="N" OR DD$="n" THEN 7310
7260 PRINT:INPUT "How many drives to test-";DD
7265 DN="":DIM DN(DD):DIM DT(DD)
7270 FOR 1=1 TO DD
7280 PRINT:INPUT "Enter drive m.rnber for drive-";DN(I)
7290 PRINT: INPUT "Enter drive type 1-1541 2-1571-";DT(I)
7300 NEXT
7310 IF MN$="N" OR MN$="n" THEN 7330
7320 A$="X":A=50:GOSUB 1140
7340 IF PT$="N" OR PT$="n" THEN 7380
7350 OPEN 1,4,7
7360 A$="E":X=10:GOSUB 3650
7370 CLOSE 1
7380 IF DD$="N" OR OO$="n" THEN 7310
7390 FOR 1=1 TO 00
186 Commodore 64 System Diagnostic Program Listing

7395 GOSUB 2990

7400 D=DN(I):T=DT(I):GOSUB 5040
7410 NEXT
7420 PS=PS+1:GOTO 7310
7430 GOSUB 299O:CLOSE 1
7440 PRINT TAB(10)"Exerciser Diagnostic":PRINT
7450 PRINT TAB(3)"Total Passes through Exerciser-";PS
7460 GOSUB 3200
7470 EX=O:GOTO 50
 Appendix B
Co._adore
System
'2.
Diillgnosliic
Pro.ra. Llirslin8
1 REM "Coomodore 128"
5 REM "System Diagnostic Program Copyright 1988
TAB BOOKS Inc."
10 POKE 2604,22:DIM K$(88):REM Set Character Set
20 DATA "inst/del","return","cursor right","f7","f1",
"f3","f6","cursor up","3"
21 DATA "w","a",1I4","z",lIs","e ll ,1I 1I,1I5",lIr","D",1I6",
"C ll , IIfll,lIt","X", 117 11 , "yll,lIglI
22 DATA "8","b","h","ull ,lIv","9",II;II,lIjll,"OIl,"n",lIk",
110 11 , IIn","+II, IIpll,lIllI, 11_11,11.11
23 DATA 1I:1I,"@II,",",II£II,II*",II;II,"clr/home ll ,1I ",11=11,
ut U,IIJII,1I1 11 ,H"II,1I ","2"
24 DATA "space"," ","Q","run stop","help","8","S",
"tab"
25 DATA "2","411,"7",1I111,"escll,II+",II_II,lIline feed"
26 "data II 11,"6 11 ,"9 11 ,"3",11 1I,"O",II.II,"Up arrow",
"down arrow","left arrow"," "
27 DATA "right arrow","no scroll"
29 FOR 1=0 TO 88: READ K$(I):NEXT
30 DIM R(8):DATA 1,2,4,8,16,32,64,128
35 FOR 1=0 TO 7:READ R(I):NEXT
36 DIM F(8):DATA 133,137,134,138,135,139,136,140

187
188 Commodore 128 BASIC Programming Differences

37 FOR A=1 TO 8:READ F(A):NEXT

40 REM "System Diagnostic Main Menu"
50 GOSUB 2990:PRINT TAB(12) "System Diagnostic":PRINT:
60 PRINT TAB(3) "<K>eyboard Text <S>eriaL Corrm Test"
70 PRINT TAB(3) "<M>onitor Test <D>isk Drive Test":
80 PRINT TAB(3) "<C>assette Test <J>oystick Test":
85 PRINT TAB(3) "<P>rinter Test <E>xerciser":
90 PRINT TAB(16) "<Q>uit":PRINT:PRINT TAB(12)
"Enter SeLection"
100 GOSUB 3000:REM Get a Key
110 IF A$="K" OR A$="k" THEN 200
120 IF A$="M" OR A$="m" THEN 800
130 IF A$="P" OR A$="p" THEN 3500
135 IF A$="C" or A$="c" THEN 4200
140 IF A$="D" OR A$="d" THEN 5000
150 IF A$="S" OR A$="s" THEN 6000
160 IF A$="E" OR A$="e" THEN 7200
165 IF A$="J" OR A$="j" THEN 7000
170 IF A$="Q" OR A$="q" THEN END
180 GOSUB 3100:GOTO 80
200 REM"Keyboard Diagnostic Module"
205 FOR 1=1 TO 8:KEY I,CHR$(F(I»:NEXT
210 POKE 2604,22:S1=1:GOSUB 630
220 A$="":KY$="":GOSUB 3000
230 N=ASC(A$)
260 IF ASC(A$)=19 THEN GOTO 740
270 IF ASC(A$)=5 THEN KY$="ctrl 2:GOTO 600
272 IF ASC(A$)=9 THEN A$=::KY$="tab":GOTO 600
273 IF ASC(A$)=(10) THEN A$="":KY$="line feed":
GOTO 600
274 IF ASC(A$)=13 THEN KY$="return":GCTO 600
280 IF ASC(AS)=17 THEN A$=" ":KYS="cursor down":
GOTO 600
290 IF ASC(AS)=18 THEN KYS="rvs on":GOTO 600
300 IF ASC(AS)=20 THEN AS=" ":KY$="inst del":GOTO 600
310 IF ASC(AS)=28 THEN KY$="ctrl 3":GOTO 600
315 IF ASC(AS)=27 THEN AS="":KY$="esc":GOTO 600
320 IF ASC(A$)';29 THEN AS=" ": KYS="cursor ri ght":
GOTO 600
330 IF ASC(AS)=30 THEN KYS="ctrl 6":GOTO 600
340 IF ASC(AS)=31 THEN KYS="ctrl 7":GCTO 600
350 IF ASC(AS)=141 THEN KY$="sh i ft return": GOTO 600
360 IF ASC(AS)=142 THEN KYS="upper case":GOTO 600
370 F ASC(AS)=144 THEN KY$="ctrl 1":GOTO 600
380 ,F ASC(A$)=145 THEN KYS=" ":KY$="cursor up":GOTO 600
390 IF ASC(AS)=146 THEN KY$="rvs off":GOTO 600
400 IF ASC(A$)=147 THEN GCTO 740
 Commodore Care Manual 189

410 IF ASC(A$)=148 THEN A$=" ":KY$="inst del":GOTO 600

420 IF ASC(A$)=156 THEN KYS="ctrl 5":GOTO 600
430 IF ASC(AS)=157 THEN AS=" ":KY$="cursor left":GOTO 600
440 IF ASC(A$)=1S8 THEN KY$="cntrl 8":GOTO 600
450 IF ASC(A$)=159 THEN KY$="ctrl 4":GOTO 600
460 IF ASC(AS)=133 THEN KY$="f1":GOTO 600
470 IF ASC(A$)=134 THEN KYS="f3":GOTO 600
480 IF ASC(AS)=135 THEN KYS="f5" :GOTO 600
490 IF ASC(AS)=136 THEN KY$="f7":GOTO 600
500 IF ASC(A$)=137 THEN KY$="f2":GOTO 600
510 IF ASC(AS)=138 THEN KYS="f4":GOTO 600
520 IF ASC(AS)=139 THEN KYS="f6":GOTO 600
530 IF ASC(A$)=140 THEN KY$="f8":GOTO 600
560 IF S=O OR S=1 THEN 600
570 IF S=2 THEN KY$="C= ":OOTO 595
580 IF S=8 THEN KY$="alt ":GOTO 595
590 KYS="ctrl/"
595 KY$=KYS+K$(K)
600 GOSUB 630
610 PRINT TAB(S) A$;TAB(13) N;TAB(23) KY$;TAB(3S) S1
620 GOTO 220
630 GOSUB 2990
640 V=PEEK(2604)
650 IF V=20 THEN S1=1:GOTO 680
660 S1=2:PRINT TAB(10) "Keyboard Diagnostic":PRINT
670 PRINT TAB(2) "Character Value Key Combination Set":
GOTO 700
680 PRINT TAB(10) "keyboard diagnostic module":PRINT
690 PRINT TAB(2) "character value key combination set"
700 PRINT TAB(2)"--------- ----- --------------- ___ II:
RETURN
710 GOSUB 630
720 PRINT "An illegal shift code was encountered!"
730 PRINT "your keyboard needs service": GOTO 220
740 POKE 2604,22:PRINT "(BLUE}":OOTO 50
800 GOSUB 299O:REM "Monitor Diagnostic Module"
810 PRINT TAB(6) "Monitor Diagnostic":PRINT
820 PRINT TAB(5) "1. .. Display Test":PRINT
830 PRINT TAB(S) "2 .•• Aligrment Test":PRINT
840 PRINT TAB(S) "3 ..• Character Set Test":PRINT
850 PRINT TAB(S) "4 .•. Color Test":PRINT
860 PRINT TAB(S) "S ••. Scroll Test":PRINT
870 PRINT TAB(S) "6 ..• Sprite Test":PRINT
890 PRINT TAB(S) "Press CLR/HOME to End Diagnostic"
900 GOSUB 3000
1000 IF ASC(AS)=19 THEN 50
1010 IF AS="1" THEN 1090
190 Commodore 728 BASIC Programming Oifferences

1020 IF AS="2" THEN 1180

1030 IF A$="3" THEN 1320
1040 IF A$="4" THEN 1440
1050 IF A$="5" THEN 1650
1070 IF A$="6" THEN 1770
1080 GOSUB 3100:GOTO 900
1090 GOSUB 2990:REM Display Character Set Test
1100 PRINT TAB(14) "Display Test":PRINT
1110 PRINT "Enter Any Character to Fill Screen":PRINT
1120 PRINT "Press CLR/Ha-1E to End Test"
1130 GOSUB 3000
1132 PRINT "(CLR/HOME}"
1135 IF ASC(A$)=19 THEN 800
1140 FOR 1=1 TO 999
1150 PRINT A$;:NEXT
1155 IF EX=1 THEN 1360
1160 GOTO 1130
1180 GOSUB 2990:REM Alignment Test
1185 POKE 2604,20
1190 PRINT TAB(13) "al ignment test":
1200 PRINT CHR$(176);:FOR 1=1 TO 18: PRINT CHRS(99);:NEXT
1210 PRINT CHR$(178);:FOR 1=1 TO 18: PRINT CHRS(99);:NEXT
1220 PRINT CHRS(174):
1230 FOR 1=1 TO 10: PRINT CHR$(98);TAB(19)CHRS(98);
TAB(38)CHR$(98):NEXT
1240 PRINT CHR$(171);:FOR 1=1 TO 18 PRINT CHRS(99);:NEXT
1250 PRINT CHRS(123);:FOR 1=1 TO 18 PRINT CHRS(99);:NEXT
1260 PRINT CHRS(179)
1270 FOR 1=1 TO 10:PRINT CHRS(98);TAB(19) CHR$(98);TAB(38)
CHR$(98):NEXT
1280 PRINT CHR$(173);:FOR 1=1 TO 18:PRINT CHRS(99);:NEXT
1290 PRINT CHR$(l77);:FOR 1=1 TO 18:PRINT CHRS(99);:NEXT
1300 PRINT CHR$(189):GOSUB 3200
1310 POKE 2604,22:GOTO 800
1320 GOSUB 2990:REM "Character Set Test"
1330 PRINT TAB(ll) "Character Set Test"
1340 PRINT:PRINT "Enter Character Set (1) or (2)-"
1350 GOSUB 3000
1360 IF A$="l" THEN POKE 2604,20
1370 FOR 1=32 TO 255
1380 IF 1=128 OR 1=130 OR 1=131 OR 1=132 OR 1=141
1=143 OR 1=144 THEN 1410
1390 IF 1=145 OR 1=146 OR 1=147 OR 1=148 OR 1=156
OR 1=157 OR 1=158 THEN 1410
1395 IF 1=159 THEN 1410
1400 PRINT CHR$(I);+" ";
1410 NEXT
 Commodore Care Manual 191

1415 IF EX=1 THEN POKE 2604,22:goto 1440

1420 PRINT:GOSUB 3200
1430 POKE 2604,22:GOTO SOO
1440 GOSUB 2990:REM "Color Test"
1450 PRINT TAB(15) "Color Test":PRINT
1460 "C$="XXXXXXXXXXXXXXXXXXXX"
1470 PRINT "(CTRL 1) Black";TAB(12) C$
1480 PRINT "(CTRL 2) lo'hite";TAB(12) C$
1490 PRINT "(CTRL 3) Red";TAB(12) C$
1500 PRINT "{CTRL 4} Cyan";TAB(12) C$
1510 PRINT "(CTRL 5) Purple";TAB(12) C$
1520 PRINT "(CTRL 6) Green";TAB(12) C$
'530 PRINT "{CTRL 7} Blue";TAB(12) C$
1540 PRINT "(CTRL B) Yellow";TAB(12) C$
1550 PRINT "(C= 1) Orange";TAB(12) C$
1560 PRINT "(C= 2) Brown";TAB(12) C$
1570 PRINT "(C= 3) Lt. Red";TAB(12) C$
15BO PRINT "{C= 4} Gray 1";TAB(12) C$
1590 PRINT "(C= 5) Gray 2";TAB(12) C$
1600 PRINT "(C= 6) Lt. Green";TAB(12) C$
1610 PRINT "(C= 7) Lt. Blue";TAB(12) C$
1620 PRINT "{C= B} Gray 3";TAB(12) C$
1625 IF EX=1 THEN PRINT "{C= 7}1I:GOTO 1680
1630 PRINT:GOSUB 3200
1640 PRINT "(C= 7}":GOTO SOD
1650 GOSUB 2990:REM "Scroll Test"
1660 PRINT TAB(15) "Scroll Test":PRINT
1670 PRINT "Enter the Nunber of Repetitions-";A:PRINT
1680 N=31
1690 FOR 1=1 TO A
1700 N=N+1:IF N>71 THEN N=32
1710 FOR X=1 TO 40
1720 PRINT CHR$(N);:N=N+1
1730 IF N>71 THEN N=32
1740 NEXT X
1750 NEXT I
1755 PRINT
1757 IF EX=1 THEN 1770
1760 GOSUB 3200
1765 GOTO BOO
1770 GOSUB 2990:REM "Sprite Test"
1780 PRINT TAB(15)"Sprite Test"
1790 FOR 1=3584 TO 4095
1S00 POKE 1,255:REM "Define Sprite Shape"
1B10 NEXT
1820 FOR X=1 TO B
1830 SPRITE X,1,2,1
192 Commodore 728 BASIC Programming Oifferences

1840 MOVSPR X,24,152

1850 MOVSPR X,90#5
1860 FOR A=1 TO 1200:NEXT A
1870 SPRITE X,O
1880 NEXT X
1915 IF EX=1 THEN RETURN
1920 PRINT:GOSUB 3200
1930 GOTO 800

2900 PRINT "(HOME/CLEAR}":RETURN:REM "Clear Screen Routine"

3000 GET A$:IF A$="" THEN 3000:REM "Get a Key Routine"
3005 K=PEEK(213):S=PEEK(211)
3010 RETURN
3100 PRINT CHR$(7):RETURN:REM "Beep Routine"
3200 PRINT TAB(7)"press any key to end test";
3210 GOSUB 3000
3220 RETURN
3300 PRINT TAB(7)"press any key to continue":RETURN

3500 REM "Printer Diagnostic Module"

3510 GOSUB 2900:PRINT TAB(11) "Printer Diagnostic":PRINT
3515 PRINT TAB(3)"1 ..• Sl iding Alpha Test":PRINT
3517 PRINT TAB(3)"2 .•• Display Character Print Test":PRINT
3518 PRINT TAB(3)"3 ..• Echo Character Print Test":PRINT
3519 PRINT TAB(3)"4 ..• Horizontal Tab Test":PRINT
3520 PRINT TAB(3)"5 ..• Line Feed Test":PRINT
3530 PRINT TAB(5)"Press CLR/HOolE to End Diagnostic
3535 OPEN 1,4,7:REM "Open as Upper/Lower case"
3540 GOSUB 3000:IF ASC(A$)<>19 THEN 3560
3550 CLOSE 1:GOTO 50
3560 IF A$="1" THEN 3630
3570 IF A$="2" THEN 3750
3580 IF A$="3" THEN 3920
3590 IF A$="4" THEN 4010
3600 IF AS="5" THEN 4070
3610 GOSUB 3100:GOTO 3540
3630 REM "Sl iding Alpha Test"
3640 GOSUB 2990:PRINT TAB(11) "Sl iding Alpha Test":PRINT
3645 INPUT "Enter the Nl.Illber of Repetitions-";X
3650 N=31
3660 FOR 1=1 TO X
3670 L$="":N=N+1:IF N>111 THEN N=32
3680 FOR A=1 TO 80
3690 L$=L$+CHR$(N):N=N+1
3700 IF N>111 THEN N=32
3710 NEXT A
3720 PRINT#1,L$;:NEXT I
 Commodore Care Manual 193

3730 IF EX=1 THEN GOTO 3760

3735 CLOSE 1
3740 GOTO 3500
3750 REM Display Character Print Test
3760 GOSUB 2990:PRINT TAB(6)"Display Character Print
Test":LS="":N=1
3770 CLOSE 1
3780 OPEN 1,4:REM "Open as Upper Case Only
3790 FOR 1=32 TO 255
3800 IF N=80 THEN PRINT#1,LS;:N=1:LS="":GOTO 3820
3810 LS=L$+CHR$(l)+" ":N=N+1
3820 NEXT I
3830 CLOSE 1
3840 OPEN 1,4,7:REM "Open as Upper/Loller case"
3850 FOR 1=32 TO 255
3860 IF N=80 THEN PRINT#1,L$;:N=1:L$="":GOTO 3880
3870 LS=LS+CHR$(I)+" ":N=N+1
3880 NEXT I
3890 IF L$<>'"' THEN PRI NT#1, L$
3900 IF EX=1 THEN GOTO 3950
3905 CLOSE 1
3910 GOTO 3500
3915 REM "Echo Character Print Test"
3920 GOSUB 2990:PRINT TAB(7)"Echo Character Print Test":
PRINT
3925 PRINT TAB(5)"Enter the Character to Echo":PRINT
3935 PRINT "Press CLR/HOME to End Test"
39£,0 GOSUB 3000: I F ASC(AS)=19 THEN CLOSE 1: GOTO 3500
3950 L$=""
3970 FOR 1=1 TO 80
3980 L$=LS+A$:NEXT
3990 PRINT#1,L$
4000 GOTO 3940
4010 REM Horizontal Tab Test
4020 GOSUB 2990:PRINT TAB(10)"Horizontal Tab Test"
4030 FOR 1=1 TO 80
4040 PRINT #1, TAB(I )"*":NEXT
4050 IF EX=1 THEN GOTO 4080
4060 CLOSE 1:GOTO 3500
4070 REM "Line Feed Test"
4080 GOSUB 2990:PRINT TAB(13)"L ine Feed Test"
4100 FOR 1=2 TO 10
4110 FOR A=1 TO I
4115 PRINT#1,"":NEXT A
4120 N$=STRS(I-1)
4130 PRINT#1,"There have been ";NS;" line feeds"; :NEXT I
4140 IF EX=1 THEN RETURN
194 Commodore 128 BASIC Programming Differences

4150 CLOSE 1:GOTO 3500

4200 REM "Cassette Diagnostic Module"

4210 GOSUB 2900
4220 PRINT TAB(10) "Cassette Diagnostic":PRINT
4230 PRINT TAB(10) "1 ... IJrite/Read Test":PRINT
4240 PRINT TAB(10) "2 ... Read Only Test":PRINT
4250 PRINT TAB(10) "Enter Ccmnand"
4260 GOSUB 3000
4270 IF A$="1" THEN 4310
4280 IF AS="2" THEN 4420
4290 GOSUB 3100
4300 GOTO 4260
4310 GOSUB 299O:PRINT TAB(13)"IJrite/Read Test":PRINT
4320 PRINT "Place a blank tape in the cassette drive"
4330 PRINT "and press RECORD.":PRINT
4340 GOSUB 3300:GOSUB 3000:PRINT
4350 OPEN 1,1,1, "Test-Tape 1"
4360 FOR 1=1 TO 100
4370 PR!NT#1,CHRS(170):NEXT
4380 CLOSE 1:OPEN 1,1, 1 ,"Test-Tape 2"
4390 FOR 1=1 TO 100
4400 PRINT#1 CHRS(85):NEXT
4405 CLOSE 1
4410 PRINT:PRINT "Rewind the tape and press PLAY"
PRINT:GOSUB 3300:gosub 3000
4415 GOTO 4460
4420 GOSUB 2990
4430 PRINT TAB(13) "Read Only Test":PRINT
4440 PRINT "Place the test tape in the cassette drive"
4450 PRINT "and press PLAY"
4455 PRINT:GOSUB 3300:GOSUB 3000:PRINT
4460 OPEN 1,1,0,"Test-Tape 1"
4470 FOR 1=1 TO 100
4480 INPUT#1,AS
4490 IF AS<>CHRS(170) THEN E=E+1
4495 NEXT
4500 CLOSE 1
4510 OPEN 1, 1,0,"Test-Tape 2"
4520 FOR 1=1 TO 100
4530 I NPUT#1 ,AS
4540 IF AS<>CHRS(85) THEN E1=E1+1
4550 NEXT I
4560 CLOSE 1:PRINT
4570 PRINT TAB(3) "There were ";E;" High Value errors"
:PRINT
 Commodore Care Manual 195

4580 PRINT TAB(3) "There were ";E1;" Low Value errors"

:PRINT
4590 GOSUB 3200
4600 GOTO 50

5000 REM: "Disk. Drive Diagnostic Module"

5010 FOR 1=1 TO 8:HVS=HV$+CHR$(170):NEXT
5020 LV$="":FOR 1=1 TO 8:LV$=LV$+CHR$(85):NEXT
5030 GOSUB 2990:PRINT TAB(10)"Disk Drive Diagnostic":PRINT
5035 INPUT "Which Drive Do You Want To Test-";D:PRINT
5036 IF D<8 OR D>15 THEN PRINT "Invalid Disk Nurrber":
GOTO 5035
5037 INPUT "Enter Drive Type 1-1541 2-1571";T
5038 IF T<>2 THEN T=1
5040 BF$=HV$:NM$="High Values"
5050 FOR 1=1 TO 2
5060 OPEN 1,D,2,"TEST,w"
5070 PRINT:PRINT"Writing ";NM$;" to Disk"
5072 IF T=2 THEN Z=33600
5074 IF T=1 THEN Z=16800
5075 FOR A=1 TO Z
5077 B1$=""
5080 PRINT#1,BF$
5090 NEXT A
5095 CLOSE 1
5100 OPEN 1,0,2, "TEST,s,r"
5110 PRINT "Reading ";NM$;" from Disk":PRINT
5115 FOR A=1 TO Z
5120 INPUT#1,BS
5140 IF B$<>BF$ THEN PRINT "Error Reading ";NMS:E=E+1
5150 NEXT
5160 CLOSE 1:SCRATCH "TEST"
5165 OPEN 15,8,15,"sO:TEST":CLOSE 15
5170 BFS=LVS:NM$="Low Values":NEXT
5172 CLOSE 1:SCRATCH "TEST"
5175 IF EX=1 THEN RETURN
5180 PRINT:PRINT "There were ";E;" errors encountered"
PRINT
5182 PRINT TAB(5)DSS:PRINT
5185 IF EX=1 THEN RETURN
5190 GOSUB 3200
5200 GOTD 50

6000 GOSUB 2990:REM "Serial Coom Module"

6010 PRINT TAB(3) "Serial COOTTIJnications Diagnostic":
PRINT
196 Commodore 128 BASIC Programming Differences

6020 PRINT TAB(7)"Press CLR/HCfolE to End Test":PRINT

6025 OOSUS 3300
6030 OOSUS 3000:GOSUB 2990
6040 OPEN 2,2,3,CHR$(6)+CHRS(0)
6050 GET #2,AS
6060 IF AS="" THEN 6070
6065 PRINT AS:
6070 GET AS:IF A$="{CLR/HCfolE}" THEN 6100
6075 IF A$="" THEN 6050
6080 PRINT#2,AS;:OOTO 6050
6100 CLOSE 2:OOTO 50

7000 DS="":DIM DS(10):GOSUB 2990:

REM "Joystick Diagnostic Module"
7002 FOR 1=1 TO 8
7004 READ DS(I):NEXT
7006 DATA "NORTH","NORTHEAST","EAST"
7007 DATA "SOUTHEAST","SOUTH"
7008 DATA "SOUTHIoIEST","'oIEST","NORTH'oIEST"
7010 PRINT TABel0) "Joystick Diagnostic":PRINT
7020 PRINT TAB(?) "Io'hich Port to Test 1 or 2-";P
7030 IF P<>2 THEN P=l
7040 PRINT:PRINT "Press Fire Button to End Test"
7050 A=JOY(P):IF A=128 OR A>128 THEN 50
7060 PRINT DS(A):OOTO 750

7200 EX=1:GOSUS 2990:REM "Exerciser Module"

7210 PRINT TAB(10)"Exerciser Diagnostic":PRINT
7220 INPUT "Test Monitor (Y or N)-";MN$:PRINT
7230 INPUT "Test Printer (Y or N)-";PTS:PRINT
7240 INPUT "Test Disk Drive(s) (Y or N)-";DDS
7250 IF DD$="N" OR DDS="n" THEN 7310
7260 PRINT:INPUT "How many drives to test-";DD
7265 DN="":DIM DN(DD):DIM DHDD)
7270 FOR 1=1 TO DO
7280 PRINT: INPUT "Enter drive nunber for drive-";DN(I)
7290 PRINT:INPUT "Enter drive type 1-1541 2-1571-";DHI)
7300 NEXT
7310 IF MN$="N" OR MNS="n" THEN 7330
7320 AS="X":A=50:OOSUB 1140
7340 IF PT$="N" OR PT$="n" THEN 7380
7350 OPEN 1,4,7
7360 AS="E":X=10:GOSUS 3650
7370 CLOSE 1
7380 IF DDS="N" OR DDS="n" THEN 7310
7390 FOR 1=1 TO DO
7395 GOSUB 2990
 Commodore Care Manual 197

7400 D=DN(I):T=DT(I):GOSUB 5040

7410 NEXT
7420 PS=PS+1:GOTO 7310
7430 GOSUB 2990:CLOSE 1
7440 PRINT TAB(10)"Exerciser Diagnostic":PRINT
7450 PRINT TAB(3)"Total Passes through Exerciser- ;PS
II

7460 GOSUB 3200

7470 EX=O:GOTO 50
 Appendix C
Ca._adara 128
BASI(e
iPragra._illlg
This book provides the System Diagnostic Program in two versions of Commodore
BASIC: one for the Commodore 64, and the other for the Commodore 128. Al-
though the two versions are very similar to one another, there are some
fundamental differences in command availability. The Commodore 128 has a
larger BASIC command set, which is summarized in this appendix. This alphabetical
summary can be used to help you convert Commodore 64 programs to run
successfully on the Commodore 128. Unless otherwise indicated, the command
is not available on the Commodore 64.

APPEND-Allows a disk file to be opened at EOF in order to add new records.

AUTO-Allows auto-numbering of BASIC programs.

BACKUP-Allows an entire disk to be copied.

BANK-Selects one of the 16 memory banks.
BEGIN/BEND-Allows a multiline set of instructions to be used with an IF-THEN
condition check.
BLOAD-Allows a binary file to be loaded from disk.
BOOT-Loads and runs a machine-language program from disk.
BOX-Draws a square or rectangle on a high-resolution screen. The Commodore
64 requires numerous PEEK and POKE instructions to accomplish this.
BSAVE-Saves a binary file to disk.
BUMP-Detects collisions between sprites. The Commodore 64 requires the
examination of a collision register located at 53278. Each sprite is represented
as a bit in the collision register. A value of 1 for the sprite's bit indicates a
collision.

198
 Glossary 199

CATALOG-Lists programs on the current disk.

CHAR-Prints a string of characters in a given location on the screen.
CIRCLE-Draws all or part of a circle or ellipse.
COLLECT-Frees up available sectors on a disk.
COLLISION-Calls up a subroutine when a sprite collision is detected. See BUMP
for the manner in which the Commodore 64 handles collisions.
COLOR-Sets screen, background, border, and foreground color. The Commodore
64 requires the POKE 53270. PEEK (53270) OR 16 instruction in conjunction
with PRINT CHR$ (X), where X is the numeric value for a particular color.
CONCAT-Combines one file into two.
COPY-Makes a copy of a disk file.

DCLEAR-Closes open disk files and clears disk channels.

DC LOSE-Closes disk files. The Commodore 64 uses the CLOSE command only.
DEC-Converts a hexadecimal number to decimal.
DELETE-Deletes a disk file.
DIRECTORY-Displays a disk's directory.
DLOAD-Loads a BASIC program from disk. The Commodore 64 uses the
instruction LOAD "filename", X where X is the drive number.
DO-Starts a DO/LOOP. Uses WHILE or UNTIL as the conditional breaks.
DOPEN-Opens a disk file. The Commodore 64 uses the OPEN command, as
in OPEN 1,8.2. "filename,W".
DRAW-Draws a line between coordinates X and Y. The Commodore 64 uses
POKE instructions to define bitmapped graphics.
OS-Returns the disk error code.
DSAVE-Saves the current program to disk. The Commodore 64 uses the SAVE
command, as in SAVE "program", X where X is the drive number.
DS$-Returns the disk status.
DVERIFY-Verifies DSAVEd disk to the program in memory. The Commodore
64 uses VERIFY to perform this function.

EL-Contains the line number of the most recent error.

ENVELOPE-Defines the shape of a sound. The Commodore 64 requires POKE
instructions to SID registers.
ER-Returns the most recent error code.
ERR$-Returns the most recent error message.
EXIT-Marks the end of a DO loop.

FAST-Causes the CPU clock to double in speed.

FETCH-Passes values from expansion memory to main memory.
FILTER-Creates sound effects. The Commodore 64 uses POKE instructions into
SI D registers.

GETKEY-Waits for a key to be pressed, and places the value into a variable. The
Commodore 64 uses a GET loop, as in GET A$:IF A$-"" THEN 10.
GO 64-Puts the system into Commodore 64 mode.
GRAPHIC-Sets the screen display mode. The Commodore 64 requires direct
POKE instructions into memory in order to set the modes.
GSHAPE-Displays a graphic shape in high-resolution mode.
200 Glossary

HEADER-Formats a blank disk. The Commodore 64 requires a disk channel

command.
HElP-Highlights the line where an error was encountered.
HEX$-Converts a decimal number into hexadecimal.

INSTR-Finds the position of a substring within a larger string.

JOY-Returns the current state of a joystick. The Commodore 64 requires direct

PEEK instructions into memory to return these values.

KEY-Controls function keys.

LOCATE-Moves the pixel cursor to the desired XY coordinates. The Commodore

64 requires a direct POKE instruction into high-resolution memory.
LOOP-See DO.

MONITOR-Turns on the machine-language monitor.

MOVSPR-Positions or moves a sprite on the screen. The Commodore 64 requires
a direct POKE instruction into sprite registers.

PAINT-Fills an area of the screen with a specific color. The Commodore 64

requires direct POKE instructions into high-resolution memory.
PEN-Returns the coordinates of the light pen. The Commodore 64 requires di-
rect PEEK instructions into memory.
PLAY-Plays a musical note. The Commodore 64 requires direct POKE instructions
into the SID registers.
POINTER-Returns the memory address of a variable.
POT-Returns information about a game paddle. The Commodore 64 requires
direct PEEK instructions into memory.

RCLR-Reads color settings. The Commodore 64 requires PEEK instructions into

memory.
RDOT-Returns the X or Y coordinate of the pixel cursor.
RECORD-Sets the record pointer to a specific record in a relative record file.
RENAME-Renames a disk file.
RENUMBER-Renumbers a BASIC program.
RESUME-Continues program execution after error trapping.
RGR-Returns the current graphic mode.
RIGHT$-Returns the right portion of a string.
RREG-Reads the 8502 registers.
RSPCOLOR-Reads the color of a sprite. The Commodore 64 requires a PEEK
instruction into the sprite register.
RSPPOS-Returns the location XY coordinates and speed of a sprite. The
Commodore 64 requires a PEEK instruction into the sprite registers.
RWINDOW-Returns the screen format information.

SCALE-Sets the high-resolution coordinate system to values given.

SCNClR-Clears the screen. The Commodore 64 uses the PRINT {CLR/HOME}"
instruction.
SCRATCH-Deletes a disk file.
SLEEP-Pauses program execution for a specified number of seconds.
 Glossary 201

SLOW-Sets the CPU clock speed to one megahertz.

SOUND-Plays a musical note. The Commodore 64 requires a direct POKE
statement into the 51 D registers.
SPRCOLOR-Sets the color of sprites. The Commodore 64 requires a direct POKE
instruction into the sprite registers.
SPRDEF-Allows definition of sprite shapes.
SPRITE-Activates and deactivates sprites. The Commodore 64 requires direct
POKE instructions into sprite registers.
SPRSAV-Transfers sprite shapes between different sprites and string variables.
SSHAPE-Places a high-resolution shape into a string variable.
STASH-Copies a section of memory into expansion memory.
SWAP-Exchanges two sections of memory.

TEMPO-Controls the time elapsed between tones being sounded. The

Commodore 64 requires POKE instructions into the SID registers.
TRAP-Prevents errors from halting a program.
TRON-Activates the BASIC trace facility used for debugging.
TROFF-Deactivates the BASIC trace facility.

UNTIL-Is used with a Do loop.

USING-Is used with PRINT to define a format for strings or numbers.

VOL-Sets the music volume. The Commodore 64 requires direct POKE

instructions into SID registers.

WHILE-Is used with a Do loop.

WIDTH-Sets the width of a point plotted on the high-resolution screen.
WINDOW-Defines a screen window.

XOR-Performs an exclusive OR on two numbers.

 Index
20 READ ERROR message, 127 writing diagnostics using, 161 system exerCiser module run on.
21 READ ERROR message, 127 basIc input/output system (BIOS), 27 153
23 READ ERROR message, 127 baud rate, 140, 141 tape interface for, 99
24 READ ERROR message, 128 beep subroutine, 6 types of, 101
25 READ ERROR message, 128 programming analysis of. 14 cassettes, 100
26 WRITE PROTECT ON message, bidirectional devices, 142 cathode ray tube (CRT), 3
128 bit map, 50 central processing unit (CPU), 2, 27
27 READ ERROR message 128 bitS, 141 character cup, 78
28 WRITE ERROR message, 129 buffer, keyboard, 28 character display modes, 35
burn In, 6, 152 switching between, 36
62 FILE NOT FOUND message, 129 bytes, 141 character generators, 50
66 ILLEGAL TRACK AND SECTOR character set test, 4, 60
message, 129 c results of, 61
cables, 24 characters (communications), 141
74 DRIVE NOT READY message, camer, 146 checksum error, 127
130 cassette diagnostic module, 6, 98-112 CHR$ code value test, 4, 36
line-by-line program analYSIS of, cleaning, 24
A 107-112 cleaning supplies, 19. 20
address jumper block, 123 listing for, 108-109 clear screen subroutine 6
addresses, disk, 124 menu for, 106 programming analYSis of, 12
adjustment potentiometers, 54 running of, 106 color monitors, 48
alignment test, 4, 59 cassette drive troubleshooting color test, 4, 60
analog noise signal, 99, 100, 138 cleaning tape head in, 105 results of. 61
anti-static sprays, 22 incorrect read/write, 103 column/row matrix (see monitors), 49
ASCII code, 36 Inoperative cassette drive, 102 command summary, Commodore
cassette drives, 1, 3, 98-112 128, 198-201
B description and function of, 99 Commodore 128 BASIC program-
backup copies, 6 head cleaning, 24 ming 198-201
BASIC, media for, 100 communication parameters, 140
system diagnostic programming running system diagnostic program communication software, 140
using 8 from, 7 compressed air, 23

202
 Index 203

CompuServe, 138 daisy chaining In. 117 I

Computext, 138 description and function of, 113 1/0 functions, 29
connectors. 25 fuse location In. 121 Incorrect color display, 54-57
head cleaning kits for. 24 integral keyboards, 28
D head-arm assembly of, 117 interface, 3
daisy chain 117 media for, 114 interface port, 144
daisy wheel, 78 operation of, 115 Internal loopback test 146
daisy-wheel printer, 77 running system diagnostic program
data size, 141 from, 7 J
Datasette, 101 system exerciser module run on, joystick d,agnostic module, 6
DELPHI, 138 153 development of, 165
demodulation, 138 types of, 114 direction test In, 169
device driver, 84 display character pnnt test, 4 58.80, fire test In, 170
diagnostic modules 82,85 flowchart for, 170, 171
deciding what to test with, 163 results of, 86 game port option in, 169
development of. 162 documentation, 16 integration of system diagnostic
integration of system diagnostiC dot-matnx printers 76 program with, 174
program and, 165 Dow Jones News 138 line-by-Ilne program analysIs for
program flowchart for, 163. 164 dust covers, 22 170-174
testing of, 165 dusting, 23, 24 listing for, 170, 172
writing BASIC version of, 164 segments of, 169
writing of. 161 testing of, 175
digital data storage, 98 E writing of, 170
digital signals, 138 echo character pnnt test, 6, 82 Joystick troubleshooting, 167
digital to analog signal conversion results of. 87
FIRE button Inoperative, 168
100 electron beam and display Image (see joystick doesn't work in particular
directionality, 142 monitors) 49
direction, 168
disk drive diagnostic module, 6, emulation. 142
Joystick inoperative, 167
113-136 etching (see monitor troubleshootrng), tests In, 169
line-by-line program analysIs of. 52 Joysticks 165
132-136 even panty, 141
FIRE button operation on, 166
listing for, 133 external disk drives, 114 function of, 165
running 01, 130 Informational sources on, 166
disk drive troubleshooting F tracking graphic objects with, 166
20 READ ERROR message In, 127 floppy, 114, 116
21 READ ERROR message in, 127 addresses In, 124 K
23 READ ERROR message, 127 contamination In. 126 kernel, 29
24 READ ERROR message in, 128 data wrrtten on, 118 key-to-contrnue subroutine, 6
25 READ ERROR message in, 128 flowcharts, 163 programming analysis of. 16
26 WRITE PROTECT ON message food and drink, 23 key-to-end-test subroutine, 6
In, 128 forms adjustment (pnnters), 80 programming analysIs of, 15
27 READ ERROR message in, 128 keyboard 1 3
28 WRITE ERROR message In, 129 description and fu nctlon of, 28
62 FILE NOT FOUNO message in, G hard-wire mapping of, 28
129 get-a key subroutine, 6
running diagnostic on, 27
66 ILLEGAL TRACK AND programming analysIs of, 13
keyboard buffer, 28
SECTOR message, 129 ghosting, 52
keyboard diagnostiC module, 4
74 DRIVE NOT READY message character display mode of, 35
in, 130 H line-by-line program analysis of,
address Jumper block in, 123 handshaking protocol, 143 38-45
cannot load program/read data file, hard copy, 3 listing for. 39
125 hard-wire mapping, 28 opening screen of, 37
cannot read or write to disk. 124 head cleaning cassette drives, 24 running of, 34
disk dnve inoperative, 120 head cleaning kits, 24 keyboard troubleshooting
fuse location in, 121 head crash. 126 filing edges of key in, 34
general guidelines lor. 119 high-resolution color graphiCS inoperative keyboard 29-32
head crash, 126 monitors, 47 mushy keys, 34
preventive maintenance for, 130 high-resolution graphics monitor, 48 particular keys Inoperative, 32-33
read data garbled, 126 higll-resolutlon monochrome removing key spring from post in
removing drive screws in, 122 graphiCS monitors, 47 35
removing metal housing In. 122 horizontal tab test. 6, 81, 87 removing keypad for, 33
disk drives, 1, 3, 113-136 results of. 88 running dlagnoslic module for, 34
204 Index

sticking keys, 33-34 o S

odd panty, 141 scroll test. 4, 57, 60
online services, 138, 139 results of, 62
L operating system, 27 scrolling, improper, 57
letter quality printers, 77 oxidation, 31 sectors, 119
line feed test, 6, 81, 88 erasing of 32 sequential access, 100
loopback connector, 148 serial bus, 27
loopback diagram, 148 serial communication Interface 1 3
p 137 ' , ,
loopback test, 6
parallel data transfer (see printers, description and function of, 137
loose cables, 24
interfaces for), 79 direct to computer, 139
parameters, communication, 140
functions of, 140
M parity, 141, 142 printers and, 138
main menu module 4 peripherals types of, 137
BASIC program~lng of, 8 basic configuration of 1, 2 serial communication Interface
general structure of. 7 learning function of, 162
diagnostic module, 6
line-by-line programming analysis reading device manual for, 162
line-by-line program analysis,
of, 8-12 receptacles for, 27 149-151
listing for, 9 tests for, 6 listing for, 150
operation of, 7 troubleshooting gUides for, 162
running of, 147
maintenance, 22 types of, 162 serial communication Interface
mass storage devices, 98 writing diagnostics for, 161-175
troubleshooting
mass storage platters, 115 pixels, 50 garbled communications, 146
misaligned displays, 53 port, interface, 144
guidelines for, 144
modem, 3,137,138 post-repair test, 152
loopback connector for, 148
communication uSing, 138 power, 25 lOOp back diagram for, 148
smart, 146 power surge protection, 23
no communications 144
status panel on, 145 power switches, 25
printer inoperative, 146
modification and adaptation, 16 preventive maintenance, 22, 23
wire bridge in, 147
modulation, 138 printer diagnostic module, 4, 76-97
serial data transfer (see printers,
modulator/demodulator, 138 line-by-line program analysIs of,
interfaces for), 79
monitor diagnostic module, 4, 46-75 88-97
sliding alpha test. 4 80, 83, 85
line-by-line program analysis of, listing for, 89-90
results of, 86
6275 operation of, 84 smart modem, 146
listing for, 64-66 printer troubleshooting
software, communications, 140
running of, 58 certain characters don't print. 82
Source, 138
monitor troubleshooting horizontal tab inoperative, 81
spares, 20
blank character location In 53 Improper paper feed, 81
sprite registers, 50
etching, 52 ' Incomplete characters, 83
sprite test, 4, 62
general guidelines for, 51 Inoperative printer, 79-80
results of, 63
ghosting, 52 installing new printer, 84
sprites, 50
high brightness lines in, 51 poor print quality, 80 Incorrect display of, 57
Improper scrolling, 57 printers, 1, 3, 76
start bits, 141, 142
incorrect color display, 54-57 cleaning, 24
startu p, 1-26
incorrect sprite display, 57 description and function of, 76
static electricity, 22
inoperative monitor, 51-52 Interfaces for, 79
stop bits, 141, 142
misaligned displays in, 53 modem Interface for, 138
subroutines, 12
particular character doesn't display, protocols for, 84
utility 6
54 system exerciser module run on
153 ' swapping out parts, 20
static on screen, 52 sync marker, 127
monitors, 1, 3, 46-75 types of, 76
syntax errors, 6
description and function of. 46 program flowchart, 163
system board, 31
function of, 48 protocols system diagnostic program, 4
interface for, 50 communications, 142
block diagram of, 5
system exerciser module run on, handshaking, 143 cassette drive running of, 7
153 printer, 84 character display mode of, 35
types of, 46 Commodore 128, BASIC program
monochrome monitors, 47 R ming for, 198-201
motherboard, 31 random access memory, 27, 100 Commodore 128, listing for,
read-only test. 106 187-197
N read-only memory devices (ROMs) Commodore 64, listing for, 176-186
numeric code test, 4 27 disk drive running of, 7
 Index 205

Installation before problems in, 7 components of, 27 upper/lowercase mode, 35

integrating custom modules with, opening of. 31 uppercase-only mode, 35
165 power supply for, 29 user resources. 21
joystick diagnostic module running diagnostic on. 27-45 user's groups, 21
integration with. 174 screw removal for. 31 utility subroutines, 6. 12
main menu for. 4, 8 listing for, 12
main menu module. listing for, 9 T
making backup copies of, 6 television set monitors, 46, 47
modification and adaptation of. 16
V
text mode. 49
vacuum/compressed air. 23
program flow and module tools and resources. 16. 17
verification, 128
summary of, 4 optional, 18
video display. 3
running of. 6 tracks, 119
tools and resources for. 16 troubleshooting and repair
utility subroutines of, 12 general guidelines for, 21 W
system exerciser module. 6 general preventive maintenance words (communications), 141
function of. 153 and. 22 write-enabling cassette tape. 104
line-by-line program analysis of, general techniques for, 25 write-protected cassette tape. 104
155-160 keyboard, 29 write-protected disk, 117, 118
listing for, 156 limits to, 21 write/read test. 106
prompts for, 155 printers, 79
running of. 154
system overview. 1 U X
system unit, 1, 2 unidirectional devices (printers), 142 XON/XOFF protocol. 142
 Commodore™ Care Manual: Diagnosing and
Maintaining Your 64 or 128 System

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Diagnosing and Maintaining Your 64 or 128 System (TAB Book No. 3141), you should definitely
consider having the ready-to-run disk containing the software applications. This software is
guaranteed free of manufacturer's defects. (If you have any problems, return the disk within 30
days, and we'll send you a new one.) Not only will you save the time and effort of typing the
programs, the disk eliminates the possibility of errors that can prevent the programs from
functioning. Interested?

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shipping and handling.

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