Displaying 16-bit Registers in Hex

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fasmnewbie

Joined: 01 Mar 2011
Posts: 555

fasmnewbie 01 Aug 2013, 15:04

I developed a macro to display/print the true HEX value of one register at a time so that I can see the immediate effect of my code. It is to be used in COM format.

Code:

org 100h
hextab db '0123456789ABCDEF'
macro prtReg a
{
        local .go, .done

        pusha
        push a
        mov bx, hextab

        mov cx, a
        xor si, si
        xchg ch, cl ;process MSB first

        .go:
        mov dl, cl
        and cl, 0Fh   ;extract nibble
        and dl, 0F0h  ;extract nibble and
        shr dl, 4     ;shift to lowest nybble
        ;Digit Translations
        mov al, dl
        xlat [bx]
        prtChar al
        mov al, cl
        xlat [bx]
        prtChar al
        inc si
        cmp si, 2
        je .done
        pop a      ;process the other half
        mov cx, a
        jmp .go

        .done:
        prtChar 'H'
        popa
}
macro prtChar a
{
     ;BIOS: Prints a character
     push ax
     mov ah, 0eh
     mov al, a
     int 10h
     pop ax
}
macro pquit
{
        mov ah,0h
        int 16h
        int 20h
}

prtReg si  ;problem buddy?
pquit

My problems are;

1. The NTVDM (Win8) complains every time I try to print SI or CS. No problem with other registers. I debugged it with the debug command and found nothing wrong with it.

2. Is there any trick to get the value of IP?

Thank you in advance for your help.

01 Aug 2013, 15:04

fasmnewbie

Joined: 01 Mar 2011
Posts: 555

fasmnewbie 01 Aug 2013, 15:33

Sample usage is:

Code:

mov bp, 16o
prtReg bp ;prints in HEX

The only problem is with SI. I suspect this has something to do with xor si, si instruction I used. But I already pushed and popped it properly. That doesn't happen with DI.

01 Aug 2013, 15:33

AsmGuru62

Joined: 28 Jan 2004
Posts: 1625
Location: Toronto, Canada

AsmGuru62 01 Aug 2013, 16:17

SI is used to do work, yet you do "pop a" and it turns into "pop si" as per macro replacement of parameters.

01 Aug 2013, 16:17

fasmnewbie

Joined: 01 Mar 2011
Posts: 555

fasmnewbie 01 Aug 2013, 16:27

AsmGuru62 wrote:

SI is used to do work, yet you do "pop a" and it turns into "pop si" as per macro replacement of parameters.

Did you mean I aliased it? I thought that a param is supposed to be a variable or a constant and that pusha should be enough in reserving si.

01 Aug 2013, 16:27

fasmnewbie

Joined: 01 Mar 2011
Posts: 555

fasmnewbie 01 Aug 2013, 16:53

Ok I got it Guru... just some minor changes.

Code:

org 100h
hextab db '0123456789ABCDEF'
macro prtReg a
{
        local .go, .done

        pusha
        ;push a
        mov bx, hextab ;for XLAT

        mov cx, a
        xor si, si
        xchg ch, cl

        .go:
        mov dl, cl
        mov dh, ch ;updated
        and cl, 0Fh   
        and dl, 0F0h 
        shr dl, 4     
        ;Digit Translations
        mov al, dl
        xlat [bx]
        prtChar al
        mov al, cl
        xlat [bx]
        prtChar al
        inc si
        cmp si, 2
        je .done
        ;pop a      
        mov cl, dh ;updated
        ;mov cx, a
        jmp .go

        .done:
        prtChar 'H'
        popa
}
macro prtChar a
{
     ;BIOS: Prints a character
     push ax
     mov ah, 0eh
     mov al, a
     int 10h
     pop ax
}
macro pquit
{
        mov ah,0h
        int 16h
        int 20h
}
;Sample usage
mov si, 4
shr si, 1
prtReg si  ;problem solved. Thanks to Guru 
pquit

01 Aug 2013, 16:53

baldr

Joined: 19 Mar 2008
Posts: 1651

baldr 01 Aug 2013, 22:13

fasmnewbie wrote:

2. Is there any trick to get the value of IP?

Use call instruction.

You may add if ~ a eq al around mov al, a inside prtChar macro to avoid otherwise perfect nop in form of mov al, al. Another improvement may be using eqtype operator to merge mov ah/al, imm8 into mov ax, imm16 for literal numeric/character argument.

There is (slow, rarely used, and unavailable in 64-bit mode) aam 16 instruction that can be used to split al into nibbles.

01 Aug 2013, 22:13

fasmnewbie

Joined: 01 Mar 2011
Posts: 555

fasmnewbie 29 Oct 2013, 15:51

baldr wrote:

fasmnewbie wrote:
2. Is there any trick to get the value of IP?
Use call instruction.

You may add if ~ a eq al around mov al, a inside prtChar macro to avoid otherwise perfect nop in form of mov al, al. Another improvement may be using eqtype operator to merge mov ah/al, imm8 into mov ax, imm16 for literal numeric/character argument.

There is (slow, rarely used, and unavailable in 64-bit mode) aam 16 instruction that can be used to split al into nibbles.

Thanks for the trick and advice.

29 Oct 2013, 15:51

jamespond

Joined: 07 Nov 2013
Posts: 1

jamespond 08 Nov 2013, 16:43

My "reg to text display" routine shows dl reg as text. It called two times:
.
.
table db "0123456789abcdef"
.
push dx
mov dl,dh
call hexout
pop dx
call hexout
.
.

hexout: mov al, dl
lea bx, table
shr al, 4
xlat
mov ah, 0eh
int 10h
mov al, dl
and al, 0fh
xlat
mov ah, 0eh
int 10h
ret

08 Nov 2013, 16:43

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