Display Hexadecimal value stored at AH

How do i display hex value stored at AH?


  • Hope you can find out
  • You must divide it in 2 nybbles (4-bit) and then process each nybble.

    Try this:

    ; Convert AH to Hex

    section .bss
    Buffer: resb 1 ; Text buffer - 1 Byte

    section .data ; Section containing initialized data
    HexStr: db "00", 10 ; 10 is EOL
    Digits: db "0123456789ABCDEF" ; Hexadecimal digits

    section .text

    global _start

    ; Read a character from stdin:
    mov eax, 3 ; sys_read call
    mov ebx, 0 ; File Descriptor 0: Standard Input
    mov ecx, Buffer ; Pass offset of the buffer to read to
    mov edx, 1 ; 1 byte to read
    int 80h ; Call sys_read

    cmp eax, 0 ; If eax=0, abort
    je Done ; Jump if equal (to 0, from compare)

    xor eax, eax ; Set eax to 0

    ; Get character from the buffer and put it in both eax and ebx:
    mov al, [Buffer] ; Put the byte from the input buffer into al
    mov ebx, eax ; Duplicate the byte in bl for second nybble

    ; Look up low nybble character and insert it into the string:
    and al, 0Fh ; Mask out all but the low nybble
    mov al, byte [Digits+eax] ; Look up the char equivalent of nyble
    mov byte [HexStr+1], al ; Write LSB char digit to line string

    ; Look up high nybble character and insert it into the string:
    shr bl, 4 ; Shift right high 4 bits of char into low 4 bits
    mov bl, byte [Digits+ebx] ; Look up char equivalent of nybble
    mov byte [HexStr], bl ; Write MSB char digit to line string

    ; Write the hexadecimal value to stdout:
    mov eax, 4 ; sys_write call
    mov ebx, 1 ; File Descriptor 1: Standard output
    mov ecx, HexStr ; Pass offset of line string
    mov edx, 3 ; Pass size of the line string
    int 80h ; Make kernel call to display line string

    mov eax, 1 ; Exit Syscall
    mov ebx, 0 ; Status Code is zero
    int 80h ; kernel call

    This example was adapted and heavily modified from the book "Assembly Language Step-by-Step - Programming with Linux, 3rd Edition" - Jeff Duntemann / Published by Wiley Publishing, Inc., Indianapolis, Indiana / ISBN: 978-0-470-49702-9

    I hope it helps! - Vasco

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