Assembly Language Programs

Program to find the larger of two
numbers.
DATA SEGMENT
A DB 34H
B DB 78H
S DB ?
DATA ENDS
CONTD..

CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START: MOV AX,DATA
MOV DS,AX
MOV AL,A
CMP AL,B ; COMPARE FIRST NO. WITH SECOND.
JNC FIRST ; JUMP IF NO CARRY (1ST NO >2ND NO.)
MOV AL,B ;1ST NO. < 2ND NO. copy 2nd no. into AL.
FIRST: MOV S,AL
INT 3
CODE ENDS
END START

Program to check whether the given
number is odd or even
Logic :
If any number is odd,
the least significant bit is ‘1’
and if even,
the least significant bit is ‘0’.
Eg: 12H :-- 00010010 EVEN
59H :-- 01011001 ODD

SHR (Shift Logical Right)
Syntax :-- SHR destination, count
•This instruction shifts the destination bit by
bit to the right and insert zeroes in the newly
introduced most significant bits.
•The shift operation is through carry.
•The count can be either 1 or specified by CL
register.
•The destination can be a byte or a word in
register or a memory location, but not an
immediate data.

BL CF
0
0
1
BL CF
0 0 0 0 0 0 1 1
• Operation Performed :--
–0  MSB ------------------ LSB  CF
• Example :--
– If CF = 0, BL = 07H
– After SHR BL, 1 ; Shift the contents of BL
register by one towards right
SHR (Shift Logical Right)Cntd..
0 0 0 0 0 1 1 1
BL = 03H

Program for odd or even
DATA SEGMENT
N DB 34H
R DB ?
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START: MOV AX, DATA
MOV DS,AX
CONTD..

MOV AL, N
SHR AL,1
JNC ev
MOV R,’O’
JMP last
ev: MOV R, ‘E’
last: INT 3
CODE ENDS
END START

Implementing a loop in assembly
language programming
• To implement a loop using LOOP instruction:
MOV CX, count
next: :
instructions
(executed ‘count’ times)
:
LOOP next
Note: LOOP instruction automatically decrements
CX register and control is transferred to label, if
CX <> 0.

Write an assembly language
program to transfer 10 bytes data
from base of data segment to base
of extra segment. Data segment
base address is 2C000H. Extra
Segment base address is DE000H.

Algorithm:
Step1: Initialize Data segment base, DS
2C00H
Step2 Initialize Extra segment base, ES
DE00H
Step3: Clear SI and DI for the offset.
Step4: Clear direction flag.
Step5: initialize counter, CX <-- 000Ah
Step6: Use string byte transfer instruction to
copy the bytes from one block to another
block (MOVSB), along with REP instruction
prefix.
Note: REP is used to repeat the instruction
execution till CX =0.

Program:
CODE SEGMENT
ASSUME CS:CODE
START: MOV AX, 2C00H
MOV DS,AX
MOV AX,DE00H
MOV ES,AX
MOV SI,0000H
MOV DI,0000H
MOV CX,000AH
CLD ;CLEAR THE DIRECTION FLAG
REP MOVSB
CODE ENDS
END START
Note: REP is used to repeat the instruction
execution till CX =0.

Write an assembly language
program to count the number of
‘1’ s in a byte.

DATA SEGMENT
N DB 56H
C DB 0H
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START: MOV AX,DATA
MOV DS,AX
MOV AL, N

MOV CX, 08H
L1: SHR AL,1
JNC NEXT
INC C
NEXT: LOOP L1
INT 3
CODE ENDS
END START

Program to find the smallest of N (9)
numbers in the array
DATA SEGMENT
ARRAY DB 0A7H,87H,34H,83H,80H,78H,0CDH,0D4H,67H
RESULT DB ?
DATA ENDS
CONTD..

CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START: MOV AX,DATA
MOV DS,AX
MOV CX,0008H
LEA BX,ARRAY
MOV AH, [BX]
BACK: INC BX
CMP AH,[BX]
JC GO ; jump if below, CF=1 same as JC
MOV AH,[BX]
GO: LOOP BACK
INC BX
MOV [BX],AH
INT 3
CODE ENDS
END START

Program to find the largest of N (9)
numbers in the array
• Note: In the above program change JB to JA
Or
• Make use of JNC

Program to arrange numbers in array
in ascending/descending order.
DATA SEGMENT
ARRAY DB 87H,67H,22H,45H,83H,80H,78H
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START: MOV AX,DATA
MOV DS,AX

MOV CL,07H ;ITERATION COUNTER
LOOP1: LEA BX,ARRAY
MOV CH,06H ; COMPARISON COUNTER
LOOP2: MOV AL, [BX]
INC BX
CMP AL,[BX]
JNC DOWN ;If 1st no is smaller, skip exchange
MOV DL,[BX] ; Exchange 2 numbers
MOV [BX],AL
DEC BX
MOV [BX],DL
INC BX
DOWN: DEC CH
JNZ LOOP2 ; if comparison counter <>0, loop2
DEC CL
JNZ LOOP1 ; if iteration counter <>0, loop1
INT 3
CODE ENDS

Program to transfer block of data from
one memory block to another
DATA SEGMENT
BLOCK1 DB 10 DUP(20H)
BLOCK2 DB 10 DUP(30H)
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START: MOV AX,DATA
MOV DS,AX
LEA SI,BLOCK1
LEA DI,BLOCK2

MOV CX,000AH
BACK: MOV AH,[SI]
MOV BH,[DI]
XCHG AH,BH
MOV [SI],AH
MOV [DI],BH
INC SI
INC DI
DEC CX
JNZ BACK
INT 3
CODE ENDS
END START

Program to transfer block of data from one
memory block to another USING STRING
INSTRUCTIONS
DATA SEGMENT
BLOCK1 DB 10 DUP(20)
BLOCK2 DB 10 DUP(20)
BLOCK 3 DB 10 DUP (?)
DATA ENDS
CODE SEGMENT
ASSUME CS:CODE, DS:DATA
START: MOV AX,DATA
MOV DS,AX
MOV ES,AX
LEA SI,BLOCK1
LEA DI,BLOCK3

LEA SI,BLOCK1 ;TRANSFER BLOCK 1 TO 3
LEA DI,BLOCK3
CLD
MOV CX,000AH
REP MOVSB
MOV CX,000AH ; TRANSFER BLOCK 2 TO 1
LEA DI,BLOCK1
LEA SI,BLOCK2
REP MOVSB
MOV CX,000AH ; TRANSFER BLOCK 3 TO 1
LEA DI,BLOCK2
LEA SI,BLOCK3
REP MOVSB
MOV AH,4CH ; END PGM:DOS INTERRUPT
INT 21H
CODE ENDS
END START