LAB EXPERIMENT # 4

Indexing and Data Manipulation

Introduction:
In this experiment you will be introduced to data transfer and arithmetic instructions.
You will also deal with indexing, and array manipulation.

Objectives:

1- Basic arithmetic instructions

2- Use of the ASCII table.
3- Manipulation of arrays

ASCII code Table:

The ASCII table is a double entry table, which contains all alphanumeric characters and
symbols. Each symbol, or character, has its own ASCII code. This code can either be in
decimal or hexadecimal format. The code of a given character is found by concatenating the
column number with the row number, if the code is to be expressed in hexadecimal. The row
number is to be the least significant. For the same code to be expressed in decimal, the row
number is added to the column number (See example given below).

As an example, the symbol’ $’ is at the intersection of row 4 and column 2, therefore its
ASCII code is 24H. The decimal equivalent of this code can be found by adding 4 to 32,
which yields 36.

The following tables show the ASCII codes (Table 4.1), and examples on the use of the
ASCII table (Table 4.2), and how to calculate the ASCII codes for different characters
and symbols.
 Table 4.1: ASCII Table

Character Column # Row # Code (H) Code (10)

a 6 1 61 96+1=97
A 4 1 41 64 + 1 = 65
β E 1 E1 224 + 1 = 225
% 2 5 25 32 + 5 = 37
Table 4.2: Examples on the use of the ASCII table

The DB and DW directives are respectively used to declare a variable of size byte or
word. The following declaration defines a variable X of size byte and assigns it the value
10H.
X DB 10H

Identically the following will define a variable of size word, and assigns it the value

13EFH: Y DW 13EFH

The DUP directive may be used to reserve more than one consecutive data item and
initialize reserved items to the same value. For example, the instruction:

ByteArray DB 100 DUP(0)

Instructs the assembler to reserve an array of 100 bytes, and initializes each byte to the
value zero. If the “0” in the above declaration is replaced with “?”, the assembler will not
initialize the bytes of the array to any value.

To access the different elements of an array, we use one of the following addressing modes
 (See Experiment # 3).

- Based addressing mode.

- Indexed addressing mode.
- Based-Indexed addressing mode.
The Based-Indexed addressing mode may be used to access a two-dimensional array.

Here are examples of each case.

Array1 DB 0,1,2,3,4,5,6,7,8,9
Array2 DB 10 DUP(0)
Array3 DB 11,12,13,21,22,23,31,32,33
RowSize EQU 3

Based addressing mode:

MOV BX, OFFSET Array1 ; Address Array1

MOV AL,[BX+4] ; Access 5th element of Array1
Indexed addressing mode:

MOV DI, OFFSET Array2 ; Address Array2

MOV [DI+6],AL ; Copy to 7th element of Array2
MOV SI,3
MOV Array2[SI],AL ;Copy to 4th element of Array2

Based-Indexed addressing mode:

MOV BX, OFFSET Array3 ; Address Array3

MOV SI,1*RowSize ; Beginning of 2nd row
MOV DI,2*RowSize ; Beginning ofrd
MOV AL, [BX+SI+1] ; Access 2nd element of 2nd row
MOV [BX+DI+2],AL ; Access 3rd element of 3rd ro
Remark:
Notice that row R, has index (R-1), and element n has index (n-1).

Pre Lab Work:

1. Study programs 4.1 and 4.2, and review the material related to indexing and data
manipulation.
2. Write both programs and see how program 4.1 manipulates the variables in internal
registers, and how program 4.2 uses memory for the same purpose.

3. Modify program 4.1 so that it adds two numbers of two digits each. Use only registers,
and make sure to take care of the carry when adding the two most significant digits. Call
this program 4.3.
Note: In this case try to understand how the program reads the numbers and how it manipulates them. This
will help you in writing your program. As a hint, one should know that numbers are given in decimal to the
program.
 4. Bring your work to the lab.

Lab Work:
1- Assemble, Link and Run program 1.

Program 1

TITLE "PROGRAM 1 EXPERIMENT 4"

; This program reads two numbers from the keyboard and

; gives their sum. This program uses internal registers

; to store the variables.

.MODEL SMALL

.STACK 200

.DATA

CRLF DB 0DH,0AH,'$'

PROMPT1 DB 'Enter the first positive integer: ','$'

PROMPT2 DB 'Enter the second positive integer: ','$'
PROMPT3 DB 'The sum of the two numbers is: ','$'

.CODE

.STARTUP

LEA DX,PROMPT1 ;DISPLAY PROMPT1

MOV AH,09H

INT 21H

MOV AH,01H ;READ FIRST NUMBER

INT 21H

SUB AL,30H ;Convert character to number

MOV CL,AL ;SAVE THE NUMBER IN CL

MOV AH,01H ;READ SECOND NUMBER

INT 21H

SUB AL,30H ;Convert character to number

ADD AL,CL ;PERFORM ADDITION AND SAVE RESULT IN CL

MOV CL,AL

ADD CL,30H ;CONVERT DIGIT TO CHARACTER

LEA DX,CRLF ;MOVE CURSOR TO NEXT LINE
MOV AH,09H

INT 21H

LEA DX,PROMPT3 ;DISPLAY PROMPT3

MOV AH,09H
 INT 21H

MOV DL,CL
MOV AH,02H
INT 21H

.EXIT
END

2- How many digits can you enter each time? Explain this.

3- What happens when the sum exceeds 9? Explain this.

4- Assemble, Link and Run program 2

Program 2:

TITLE "PROGRAM 2 EXPERIMENT 4"

; This program reads two numbers from the keyboard and

; displays their sum. This program uses the memory to

; store the variables.

. MODEL SMALL

.STACK 200

.DATA

CRLF DB 0DH,0AH,'$'

PROMPT1 DB 'Enter the first positive integer: ','$'

PROMPT2 DB 'Enter the second positive integer: ','$'
PROMPT3 DB 'The sum of the two numbers is: ','$'

NUM1 DB ?
NUM2 DB ?
RES DB ?

.CODE
 COAL Lab Manual

.STARTUP

LEA DX,PROMPT1 ;DISPLAY PROMPT1

MOV AH,09H

INT 21H

MOV AH,01H ;READ FIRST NUMBER

INT 21H

SUB AL,30H ;Convert character to number

MOV NUM1,AL ;SAVE NUM1

LEA DX,CRLF ;MOVE CURSOR TO NEXT LINE

MOV AH,09H
INT 21H

LEA DX,PROMPT2 ;DISPLAY PROMPT2

MOV AH,09H

INT 21H

MOV AH,01H ;READ SECOND NUMBER

INT 21H

SUB AL,30H ;Convert character to number

MOV NUM2,AL ;SAVE NUM2

ADD AL,NUM1 ;PERFORM ADDITION

MOV RES,AL ;SAVE RESULT IN RES

LEA DX,CRLF ;MOVE CURSOR TO NEXT LINE

INT 21H

LEA DX,PROMPT3 ;DISPLAY PROMPT3

MOV AH,09H

INT 21H

;DISPLAY SUM

MOV DL,RES ;RETREIVE RES FROM MEMORY

ADD DL,30H ;CONVERT DIGIT TO CHARACTER

.EXIT END
5. Repeat step 4 with program 3.

6. Show all your work to the instructor.

7. Submit all your work at the end of the lab session.

3. Assemble, Link and Run program

Program 3:

Program 2 modified version

TITLE TWO_DIGIT_ADDITION
.MODEL SMALL
.STACK 100H
.DATA
DIGIT1 DB 0AH, 0DH, "ENTER FIRST DIGIT: $"
DIGIT2 DB 0AH, 0DH, "ENTER SECOND DIGIT: $"
RESULT DB 0AH, 0DH, "RESULT IS $"
.CODE
MAIN:
MOV AX, @DATA
MOV DS, AX

LEA DX, DIGIT1

MOV AH, 09H
INT 21H

MOV AH, 01H

INT 21H

SUB AL, 30H

MOV BH, AL

MOV AH, 01H

INT 21H

SUB AL, 30H

MOV BL, AL ; BH:BL FIRST NUMBER

LEA DX, DIGIT2

MOV AH, 09H
INT 21H

MOV AH, 01H

INT 21H

SUB AL, 30H

MOV CH, AL

MOV AH, 01H

INT 21H
 SUB AL, 30H
MOV CL, AL ; CH:CL SECOND NUMBER

ADD BL, CL

MOV AL, BL
MOV AH, 00H
AAA

MOV CL, AL ; LAST DIGIT OF ANSWER

MOV BL, AH

ADD BL, BH
ADD BL, CH

MOV AL, BL
MOV AH, 00H
AAA

MOV BX, AX
;MOV BH, AH
;MOV BL, AL

MOV DX, OFFSET RESULT

MOV AH, 09H
INT 21H

MOV DL, BH
ADD DL, 30H
MOV AH, 02H
INT 21H

MOV DL, BL
ADD DL, 30H
MOV AH, 02H
INT 21H

MOV DL, CL
ADD DL, 30H
MOV AH, 02H
INT 21H
EXIT:
MOV AH, 04CH
INT 21H
END MAIN

Lab Assignment
1. Write a program to check input number is even or odd.
2. Write a program in assembly language to find the
Square of a given number.
3. Write a program to print an array with loop
4. Write a program to print an array without loop
5. Explain the use of “DUP” in assembly language through a code.