8086 program to Subtract two 16 bit numbers

03:52


ØØ       Explanation :
·            Consider that a word of data is present in the AX register and second word of data is present in the BX register.
·            We have to subtract the word in BX with the word AX.
·            Using subtract (SUB) instruction, subtract the contents of two registers.
·            Result will be stored in the AX register.
·            Display the result using display routine.
AX = 1234 H

1234 H
BX = 0100 H
–
0100 H


1134 H
ØØ       Algorithm :
Step I       :    Initialise the data segment.
Step II     :    Get the first number in AX register.
Step III   :    Get the second number in BX register.                        
Step IV    :    Add the two numbers.
Step V     :    Display the result.
Step VI    :    Stop
ØØ       Flowchart : Refer flowchart
ØØ       Program :
.model small
.data
a dw 1234H                                                
b dw 0100H
.code
       mov     ax, @data               ; Initialize data section
       mov     ds, ax 
       mov     ax, a                      ; Load number1 in ax
       mov     bx, b                     ; Load number2 in bx
       sub      ax, bx                    ; subtract numbers. Result in ax
       mov     ch, 04h                  ; Count of digits to be displayed
       mov     cl, 04h          ; Count to roll by 4 bits
       mov     bx, ax                    ; Result in reg bx
l2:    rol       bx, cl                     ; roll bl so that msb comes to lsb
       mov     dl, bl                     ; load dl with data to be displayed
       and      dl, 0fH          ; get only lsb
       cmp     dl, 09                    ; check if digit is 0-9 or letter A-F
       jbe       l4
       add      dl, 07                    ; if letter add 37H else only add 30H
l4:    add      dl, 30H
       mov     ah, 02                    ; Function 2 under INT 21H (Display character)
       int       21H
       dec      ch                         ; Decrement Count
       jnz       l2
       mov     ah, 4cH                  ; Terminate Program
       int       21H
       end
ØØ       Result :
C:\programs>tasm 16-sub.asm
Turbo Assembler  Version 3.0  Copyright (c) 1988, 1991 Borland International
Assembling file:   16-sub.asm
Error messages:    None
Warning messages:  None
Passes:            1
Remaining memory:  438k
C:\programs>tlink 16-sub.obj
Turbo Link  Version 3.0 Copyright (c) 1987, 1990 Borland International
Warning: No stack
C:\programs>16-sub
1134