Question

3) Write a simple 8086 assembly program that:
- Load AL by an arbitrary number,
- Check whether it is an odd/even number,
- If it is an odd number, it will be converted to its next larger even number and will be shown in port 0 in the trainer kit.
- If it is an even number, it will be converted to its previous smaller odd number and will be shown in port 0 in the trainer kit.

Answer 1

Here is a possible solution:

.MODEL SMALL
.STACK 100h

.DATA
number DB 17 ; the arbitrary number to work with

.CODE
MOV AX, @DATA ; initialize DS
MOV DS, AX

MOV AL, number ; load AL by the arbitrary number

AND AL, 01h ; check the least significant bit (LSB)
JZ even ; if it is zero, AL is even
; if it is one, AL is odd
ADD AL, 1 ; convert AL to the next larger even number
JMP show_result

even:
SUB AL, 1 ; convert AL to the previous smaller odd number

show_result:
MOV AH, 0 ; clear AH (not needed, but good practice)
MOV DX, 0 ; prepare DX for the OUT instruction
MOV DX, 8 ; select port 0 in the trainer kit (use your own value)
MOV BL, AL ; move the result to a safe place (optional)
OUT DX, AL ; send the result to port 0

MOV AH, 4Ch ; return control to DOS
INT 21h

END