Program for Simulating AAA Instruction

May 4, 2011 by ProjectsGeek Leave a Comment

Objective

Write a Program for Simulating AAA Instruction in assembly language.

AAA instruction stands for ASCII Adjust for Addition. It is used whenever we want to add two decimal digits which are Representative in ASCII code, without masking off “3” in upper nibble. In our program AAA instruction is not available in the instruction set of 8086. So we will first accept the two digits in AL and BL registers. Then we will mask the upper nibble i.e. “3” from AL and BL register by ANDing with 0F H, so that we will get LSB of two numbers. Then the two numbers are added.

Result of addition is in AL. We will check if the result is valid BCD. If addition > 9, then result is invalid BCD and to make it valid we will add 6. If result is valid, display the result.

Algorithm for Simulating AAA Instruction

Step I : Initialize the data segment.

Step II : Load number 1 in AL.

Step III : Load number 2 in BL.

Step IV : Mask the number 1 and store result in AL.

Step V : Mask number 2 and store result in BL.

Step VI : Add = number 1 + number 2.

Step VII : Check if addition < 9. If yes go to step IX. else go to step VIII.

Step VIII : Add 6 to make the result valid.

Step IX : Display the result.

Step X : Stop.

Program for Simulating AAA Instruction 1

Program for Simulating AAA Instruction

 .model small  
 .data  
 a db 39H  
 b db 32H  
 .code  
      mov      ax, @data           ; Initialize data section  
      mov      ds, ax  
      mov      al, a               ; Load number1 in al  
      mov      bl, b               ; Load number2 in bl  
      and      al, 0fh             ; unmask numbers and result in al  
      and      bl, 0fh             ; unmask numbers and result in al  
      add      al, bl              ; add the numbers in al and bl   
      cmp      al, 09h             ; check if no is valid BCD   
      jb      next  
      add      al, 06h             ; for invalid BCD add 6 to        
                                   ; make it valid  
 next:      mov      ch, 02h       ; Count of digits to be        
                                   ; displayed  
      mov      cl, 04h             ; Count to roll by 4 bits  
      mov      bh, al              ; Result in reg bh  
 l2:     rol      bh, cl           ; roll bl so that msb comes   
                                   ; to lsb   
      mov      dl, bh              ; 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

How to Run this Program

For Running this program you should have installed Tasm on you computer . If you have not installed Tasm yet please install from Here .

C:\programs>tasm aaa.asm
Turbo Assembler  Version 3.0  Copyright (c) 1988, 1991 Borland International
Assembling file:   aaa.asm
Error messages:    None
Warning messages:  None
Passes:            1
Remaining memory:  438k
C:\programs>tlink aaa
Turbo Link  Version 3.0 Copyright (c) 1987, 1990 Borland International
Warning: No stack
C:\programs>aaa
11

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