See discussions, stats, and author profiles for this publication at: https://www.researchgate.

net/publication/291773586

PLC with PIC16F648A microcontroller (part 1)

Article  in  ELECTRONICS WORLD · November 2008

CITATION READS

1 7,456

1 author:

Murat Uzam
Yozgat Bozok University
150 PUBLICATIONS   2,053 CITATIONS   

SEE PROFILE

Some of the authors of this publication are also working on these related projects:

An Image Interpreter for Vision-Based Logic Control of Manufacturing Plant View project

Analog Input / Analog Output Modules for a 5V Microcontroller Based PLC View project

All content following this page was uploaded by Murat Uzam on 20 August 2017.

The user has requested enhancement of the downloaded file.

 Volume 114, Issue 1871

9 770959 833110 11

NOVEMBER 2008 £4.60

www.electronicsworld.co.uk

THE ESSENTIAL ELECTRONICS ENGINEERING MAGAZINE

Special Issue –
Microcontrollers:
• BUILD YOUR OWN DATA LOGGER
• BUILD YOUR OWN MCU-BASED PLC
• CHOOSING BETWEEN ARM7 AND CORTEX-M3

PURCHASING
NEW OSCILLOSCOPES?
CONSIDER THE UPDATE
RATES!

TECHNOLOGY UKDL PRODUCTS

LEARNING RIGHT LASER COMMS TEST SYSTEMS,
FROM FOR THE POSTERS AND
NATURE RIGHT JOB ANALYSERS

ALSO IN THIS ISSUE: THE TROUBLE WITH RF: SO MANY TRANSMITTERS, SO SMALL A BAND
 Electronics World CONTENTS

05 EDITOR’S COMMENT
Issue 1871
Volume 114,

11
9 770959 833110
2008 £4.60
NOVEMBER world.co.uk
www.electronics

CALL FOR ARTICLES AND ARTICLE GUIDELINES THE ESSENT

IAL ELECTR
ONICS ENGINE
ERING MAGAZI
NE

Page 17 - the place

–
to find more about
06 TECHNOLOGY Special Issue s:
Microcontrol
ler
OWN DATA LOGGE
R
Microchip's mTouch
Sensing Solutions
• BUILD YOUR
YOUR OWN MCU-B
ASED PLC
• BUILD SING EN ARM7 AND
CORTEX-M3
• CHOO BETWE

09 NEW READER OFFER PURCHASING

NEW OSCILLOSC
CONSIDER THE
OPES?
UPDATE

RATES!

PRODUC TS

11 FOCUS
SYSTEM S,
UKDL COMMS TEST
POSTERS AND
TECHNO LOGY RIGHT LASER ANALYS ERS
LEARNING FOR THE
FROM RIGHT JOB
NATURE A BAND
SO SMALL
TRANSMITTERS,
SO MANY
TROUBL E WITH RF:
ISSUE: THE
ALSO IN THIS

CRACKING THE CRACKERS

by Steve Rogerson FEATURES
13 ROHS
Gary Nevison answers readers’ questions relating to the
18 CHOOSING ARM PROCESSOR ARM7 VS
CORTEX-M3
RoHS, REACH, WEEE and EuP directives
Anders Lundgren considers the criteria when
making the choice of microcontrollers based
14 INSIGHT
on the ARM Cortex-M3 core
TAIWANESE ICT INDUSTRY FORECAST IN 2008
by Katie Chen
21 PLC WITH PIC16F648A
MICROCONTROLLER PART 1
15 THE TROUBLE WITH RF…
Dr Murat Uzam kick-starts a series of articles
SO MANY TRANSMITTERS, SO SMALL A BAND
on a project that focuses on microcontroller-
by Myk Dormer
based PLCs

26 MICROCONTROLLER AND SD-CARD BASED

MULTICHANNEL DATA LOGGER

21
Dogan Ibrahim describes the design of a
microcontroller-based multichannel data
logger device with SD card and real-time clock
interface

32 OSCILLOSCOPE UPDATE RATE AND ITS

6 IMPACT ON CAPTURING INFREQUENT
AND RANDOM EVENTS
Johnnie Hancock and Joel Woodward look
at update rates as one of the primary
REGULARS considerations when purchasing a new
oscilloscope
35 CIRCUIT IDEAS

39 UKDL
Dr Ric Allott reviews some of the fundamental
properties of lasers and how these properties influence
the choice of laser for a particular manufacturing
operation

42 TIPS ‘N’ TRICKS

45 PRODUCTS 26 32
www.electronicsworld.co.uk Electronics World - November 08 ❙ 3
UZAM 16/9/08 10:25 Page 36

Feature PLC/MCU

PLC WITH PIC16F648A

MICROCONTROLLER
(PART 1) ASSOCIATE PROFESSOR DR MURAT UZAM
FROM NIGDE UNIVERSITY IN TURKEY
The Series KICK-STARTS A SERIES OF ARTICLES ON A
The articles to be published are as PROJECT THAT FOCUSES ON A
follows: MICROCONTROLLER-PLC
1. The Hardware: Run in this issue.
2. The Basic Software: This article explains the basic software 9. Logical Macros: The following logical macros are described in this
structure of the UZAM_PLC. A PLC scan cycle includes the following: article: inv_R, AND, NAND, OR, NOR, XOR, XNOR. These macros are
1. obtain the inputs, 2. run the user program, 3. update the outputs. applied to an 8 bit register (R1) with another register (R2) or an 8 bit
In addition, it is also necessary to define and initialise all variables constant (K).
used within a PLC. Necessary functions are all described as PIC 10. Shift&Rotate Macros: The following Shift&Rotate macros are
Assembly macros to be used in UZAM_PLC. The macros described in described in this article: SHIFT_R (shift right the contents of register R),
this article could be summarised as follows: “HC165” (for handling the SHIFT_L (shift left the contents of register R), ROTATE_R (rotate right
inputs), “HC595” (for sending the outputs), “dbncr” (for debouncing the the contents of register R), ROTATE_L (rotate left the contents of
inputs), “initialise”, “get_inputs”, “send_outputs”. register R), SWAP (swap the nibbles of the register).
3. Contact and Relay Based Macros: The following contact and relay 11. Multiplexer Macros: The following multiplexer macros are
based macros are described in this article: ld (load), ld_not (load_not), described in this article: mux_2_1 (2x1 MUX), mux_2_1_E (2x1 MUX
not, or, or_not, nor, and, and_not, nand, xor, xor_not, xnor, out, out_not, with Enable input), mux_4_1 (4x1 MUX), mux_4_1_E (4x1 MUX with
in_out, inv_out, set, reset. These macros are defined to operate on one Enable input), mux_8_1 (8x1 MUX), mux_8_1_E (8x1 MUX with Enable
bit variables. input).
4. Flip-Flop Based Macros: The following flip-flop based macros are 12. DeMultiplexer Macros: The following demultiplexer macros are
described in this article: r_edge (rising_edge), f_edge (falling_edge), described in this article: Dmux_1_2 (1x2 DMUX), Dmux_1_2_E (1x2
latch0, latch1, dff_r (rising edge triggered D flip-flop), dff_f (falling DMUX with Enable input), Dmux_1_4 (1x4 DMUX), Dmux_1_4_E (1x4
edge triggered D flip-flop), tff_r (rising edge triggered T flip-flop), tff_f DMUX with Enable input), Dmux_1_8 (1x8 DMUX), Dmux_1_8_E (1x8
(falling edge triggered T flip-flop), jkff_r (rising edge triggered JK flip- DMUX with Enable input).
flop), jkff_f (falling edge triggered JK flip-flop). 13. Decoder Macros: The following decoder macros are described in
5. Timer Macros: The following timer macros are described in this this article: decod_1_2 (1x2 decoder), decod_1_2_E (1x2 decoder with
article: TON_8 (ON delay timer), TOF_8 (OFF delay timer), TEP_8 Enable input), decod_2_4 (2x4 decoder), decod_2_4_E (2x4 decoder
(Extended Puls timer), TOS_8 (Oscillator timer). with Enable input), decod_3_8 (3x8 decoder), decod_3_8_E (3x8
6. Counter Macros: The following counter macros are described in this decoder with Enable input).
article: CTU_8 (Up Counter), CTD_8 (Down Counter), CTUD_8 (Up/Down 14. Priority Encoder Macros: The following priority encoder macros
Counter). are described in this article: encod_4_2_p (4x2 priority encoder),
7. Comparison Macros: The following comparison macros are encod_4_2_p_E (4x2 priority encoder with Enable input), encod_8_3_p
described in this article: The contents of two registers (R1 and R2) are (8x3 priority encoder), encod_8_3_p_E (8x3 priority encoder with
compared according to the following: GT (Greater Than – “>”), GE Enable input), encod_dec_bcd_p {decimal to BCD (Binary Coded
(Greater than or Equal to – “≥”), EQ (EQual to – “=”), LT (Less Than – Decimal) priority encoder}, encod_dec_bcd_p_E (decimal to BCD
“<”), LE (Less than or Equal to – “≤”), NE (Not Equal to – “≠”). Similar priority encoder with Enable input).
comparison macros are also described for comparing the contents of 15. An Example: This article describes an example of a remotely-
an 8 bit register (R) with an 8 bit constant (K). controlled model gate system and makes use of UZAM_PLC to control
8. Arithmetical Macros: The following arithmetical macros are it for different control scenarios.
described in this article: The following operators are applied to the
contents of two registers (R1 and R2): ADD, SUB (subtract), INC The reader is expected to be familiar with PLCs, PIC microcontrollers
(increment), DEC (decrement). Similar arithmetical macros are also and PIC Assembly language. UZAM_PLC macros are developed by using
described to be used with the contents of an 8 bit register (R) and an 8 PIC Assembly language. The program development environment used is
bit constant (K). that of MPLAB IDE (www.microchip.com).

www.electronicsworld.co.uk Electronics World - November 08 ❙ 21

UZAM 16/9/08 10:25 Page 37

PLC/MCU Feature

Figure 1: The schematic diagram of the UZAM_PLC main board

rogrammable Logic Controllers UZAM_PLC with PIC16F648A. First in the macros. In addition, many new features

P (PLCs) have been extensively used

in industry for the past five or six
decades. PLC manufacturers offer different
series is this article, which describes the
hardware of UZAM_PLC with PIC16F648A.
have been included within UZAM_PLC
project to make it more of an engulfing
PLC. However, this project does not include
devices in terms of functions, program DESIGN AND graphical interface PC software as in PICBIT
memories and the number of IMPLEMENTATION or in other PLCs for developing PLC
inputs/outputs (I/O), ranging from a few to This project has been completed in search programs. Rather, PLC programs are
thousands of I/Os. for how to design and implement a PLC. developed by using macros as done in the
The design and implementation of PLCs Some ideas can be found in the freely Instruction List (IL) PLC programming
have long been a secret of the PLC available PLC project called “PICBIT” from language. An interested and skilled reader
manufacturers. As a microprocessor-based around 10 years ago. An Internet search could well – and encouraged to – develop
technology, the functionality of a PLC is for the keyword “PICBIT” leads to this graphical interface PC software for easy
well known from the end-user/programmer project. use of UZAM_PLC.
point of view, but by now no serious work PICBIT describes a PIC16F84
has been reported to describe a microcontroller based PLC with five THE HARDWARE WITH
microprocessor/microcontroller based discrete inputs and eight discrete outputs. PIC16F648A
implementation of a PLC. The file called “picbit.inc” of the PICBIT The hardware of UZAM_PLC with
With a series of articles I aim to describe contains the basic PLC macro definitions. PIC16F648A consists of two parts: “main
a PIC microcontroller based design and The UZAM_PLC project has been board” and “I/O extension board”. The
implementation of a PLC, called completed by the inspiration of these schematic diagram of UZAM_PLC main

22 ❙ November 08 - Electronics World www.electronicsworld.co.uk

UZAM 16/9/08 10:25 Page 38

Feature PLC/MCU

Figure 2: The schematic diagram of the UZAM_PLC I/O extension board

board is shown in Figure 1. The main Electronics World for details). PIC16F648A microcontroller. Although it
board contains mainly five sections: power, For other types of USB or parallel port can run up to 20MHz, in UZAM_PLC it is
programming, CPU (Central Processor PIC programmers the reader is expected to fixed to run at 4MHz with its internal
Unit), inputs and outputs. make necessary arrangements. ICSP oscillator. This frequency is fixed because
The power section accepts 12V AC input connector takes the lines VPP(MCLR), VDD, time-delays are calculated based on this
and produces as outputs 12V DC to be VSS(GND), DATA (RB7), CLOCK (RB6) from speed. However, by means of two
used as the operating voltage of relays, the PIC programmer hardware through a switches, namely SW1 and SW2, it is also
and 5 V DC to be used for ICs, inputs, etc. properly prepared cable and it serves them possible to use an external oscillator with
The programming section deals with the to a 4PDT (four pole double throw) switch. different crystal frequencies. When doing
programming of PIC16F648A There are two positions of the 4PDT so, time-delay functions must be calculated
microcontroller. For programming the switch. As seen in Figure 1, in one position accordingly. SW3 directs the RA5 pin either
PIC16F648A in circuit, it is necessary to use of 4PDT switch, PIC16F648A is ready to be to one pole of 4PDT switch or to the future
a PIC programmer hardware and software programmed and in the other position the extension connector.
with ICSP (In Circuit Serial Programming) loaded program is run. For properly
capability. For those who have a PC with programming the PIC16F648A by means of PROGRAMMING PICS
serial port, PCB files for a PIC programmer a PIC programmer and the 4PDT switch, it When programming PIC16F648A, RA5
hardware, called JDM programmer, and is also a necessity to switch off the power should be connected to 4PDT switch. RB0,
related software can be downloaded switch. RB6 and RB7 pins are all reserved to be
(please contact the editorial office of The CPU section consists of the used for an 8-bit parallel to serial converter

www.electronicsworld.co.uk Electronics World - November 08 ❙ 23

UZAM 16/9/08 10:25 Page 39

PLC/MCU Feature

register 74HC/LS165. Through these three PIC16F648A provides the following: DC signals. These external input signals are
pins and with added 74HC/LS165 registers 4096 words of Flash program memory; 256 isolated from the other parts of the
we can describe as many inputs as we bytes of RAM data memory and 256 bytes hardware by using NPN type opto-couplers
wish. RB0, RB6, and RB7 are the “data in”, of EEPROM data memory. The UZAM_PLC (e.g. 4N25). For simulating input signals,
the “clock in” and the “shift/load” pins, macros make use of registers defined in one can use on board push-buttons as
respectively. RAM data memory. Note that it may be temporary inputs and slide switches as
Similarly, RB3, RB4 and RB5 pins are all possible to use PIC16F628A as the CPU, permanent inputs.
reserved to be used for 8-bit serial to but one has to bear in mind that In the beginning of each PLC scan cycle
parallel converter register/driver TPIC6B595. PIC16F628A provides the following: 2048 (get_inputs) 74HC/LS165 is loaded (RB7
Through these three pins and with added words of Flash program memory; 224 bytes (shift/load) = 0) with the level of 8 inputs
TPIC6B595 registers we can describe as of RAM data memory and 128 bytes of and then this data is serially clocked in
many outputs as we wish. RB3, RB4 and EEPROM data memory. (when RB7 = 1; through RB0 “data in” and
RB5 are the “clock out”, the “data out” In this case it is necessary to take care of RB6 “clock in” pins). If there is no I/O
and the “latch out” pins, respectively. The the usage of RAM data memory. The extension board used, then 8 clock_in
remaining unused pins of the PIC16F648A inputs section introduces 8 discrete inputs signals are enough to get the 8 input
are connected to the “future extension for the UZAM_PLC, called I0.0, I0.1, ..., signals. For each I/O extension board, 8
connector”. I0.7. Each input can accept 5V DC or 24V more clock_in signals are necessary.

A B C

D E

Figure 3: Photographs of (a) the UZAM_PLC main board, (b) UZAM_PLC I/O extension board, (c) UZAM_PLC main board with a PIC
programmer, (d) UZAM_PLC main board plus an I/O extension board and a USB PIC programmer, (e) UZAM_PLC main board plus two
I/O extension boards and a USB PIC programmer
UZAM 17/9/08 14:48 Page 40

Feature PLC/MCU

DATA INPUT As shown in Figure 2, the “I/O extension board” contains mainly
The serial data coming from the I/O extension board is taken from two sections: discrete inputs (8 of them) and discrete outputs (also
the “SI” input of 74HC/LS165. The outputs section introduces 8 8 of them). They are similar to the ones as described for the main
discrete relay outputs for the UZAM_PLC, called Q0.0, Q0.1, ..., board.
Q0.7. Each relay operates with 12V DC and is driven by an 8-bit The I/O extension connector “DB9M” seen on the left connects
serial to parallel converter register/driver TPIC6B595. the I/O extension board to the main board or to a previous I/O
Relays have SPDT (single pole double throw) contacts with C extension board. Similarly, the I/O extension connector “DB9F”
(common), NC (normally closed) and NO (normally open) terminals. seen on the right connects the I/O extension board to an adjacent
At the end of each PLC scan cycle (send_outputs) the output data I/O extension board. In this way we can connect as many I/O
is serially clocked out (through RB3 “clock out” and RB4 “data extension boards as necessary. The 12V DC power is taken from
out” pins) and finally latched within TPIC6B595. If there is no I/O the main board or from a previous I/O extension board and it is
extension board used, then 8 clock_out signals are enough to send passed to the next I/O extension boards.
the 8 output signals. For each I/O extension board, 8 more The 5V DC voltage is taken from the main board or from a
clock_out signals are necessary. previous I/O extension board through the “DB9M” connector and it
The serial data going to the I/O extension board is sent out from is passed on to the next I/O extension boards through the “DB9F”
the “SER OUT” (pin 18) of TPIC6B595. In addition, there is also an connector. The PCB design files of the I/O extension board can be
I/O extension connector “DB9F” for conveying the I/O data to and had from the editorial offices of the magazine. Note that in the
from all the connected extension I/O boards. The PCB design files PCB design of the I/O extension board, some lines of I/O extension
of the main board can be received from the editorial offices of connectors “DB9M” and “DB9F” are different from the ones
Electronics World. Note that in the PCB design of the main board, shown in Figure 2. Figure 3 is a selection of photos of the
some lines of I/O extension connector are different from the ones UZAM_PLC main board and I/O extension board with and without a
shown in Figure 1. PIC programmer. ■

www.electronicsworld.co.uk Electronics World - November 08 ❙ 25

View publication stats