Question

Write an 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

Assuming we are using an ASCII code representation for the numbers to be shown in port 0, here's an example program:

```
; The arbitrary number is loaded in AL by the BIOS or other program.

start:
; Check whether AL is odd or even.
mov bl, 2 ; BL = 2 (the divisor for even/odd check)
xor ah, ah ; Clear AH to prepare for division
div bl ; Divide AL by BL, remainder is in AH

; Check the remainder: if it's zero, AL is even; otherwise, it's odd.
cmp ah, 0
je even
; AL is odd - convert to next larger even number.
add al, 1

odd:
; Convert the number to ASCII and show it in port 0.
add al, 30h ; Convert to ASCII digit
mov ah, 1
mov cx, 1
int 21h ; Use DOS interrupt for serial port output
jmp end

even:
; Convert the number to previous smaller odd number.
sub al, 1

; Skip output if AL is negative (no odd number below 1).
cmp al, 0
jl end

; Convert the number to ASCII and show it in port 0.
add al, 30h ; Convert to ASCII digit
mov ah, 1
mov cx, 1
int 21h ; Use DOS interrupt for serial port output

end:
; End of program.
ret
```