Tutorial: Convert byte to hex

Code:

org 100h

macro print_digit
{
mov bx,digits
add bx,ax
mov ah,2
mov dl,[bx]
int 21h
}

macro print_nibble
{
xor ch,ch
shl cx,4
xor ax,ax
or al,ch
print_digit
}

mov cx,0efh     ; Byte to convert
rept 2 { print_nibble }
int 20h

digits db '0123456789ABCDEF'

With macro expansions:

Code:

org 100h

;macro print_digit
;{
; mov bx,digits
; add bx,ax
; mov ah,2
; mov dl,[bx]
; int 21h
;}

;macro print_nibble
;{
; xor ch,ch
; shl cx,4
; xor ax,ax
; or al,ch
; print_digit
;}

mov cx,0efh
;rept 2{print_nibble}
;print_nibble
xor ch,ch
shl cx,4
xor ax,ax
or al,ch
;print_digit
mov bx,digits
add bx,ax
mov ah,2
mov dl,[bx]
int 21h
;print_nibble
xor ch,ch
shl cx,4
xor ax,ax
or al,ch
;print_digit
mov bx,digits
add bx,ax
mov ah,2
mov dl,[bx]
int 21h
int 20h

digits db '0123456789ABCDEF'

This code has been revised as follows: (thanks to AsmGuru62)

Code:

org 100h
macro print_nibble {
xor ch,ch
shl cx,4
mov al,ch
cmp al,10
sbb al,69h
das
int 10h
}
mov cx,0efh     ; Byte to convert
mov ah,0eh
rept 2 {print_nibble}
int 20h

; ; input: ; al = single hex digit ; ; output: ; al = single ASCII digit ; ; destroys: ; flags ; cmp al,10 ; if x < 10, set CF = 1 sbb al,69h ; 0-9: 96h .. 9Fh, A-F: A1h..A6h das ; 0-9: subtr. 66h -> 30h-39h, ; A-F: subtr. 60h -> 41h..46h