ah and al registers query

[newbieatassembly]

Hi,

I was just trying to do
asm {
mov ah, 0x00
mov ax, 0x13
int 0x10
}

It looks as though I don't have to set ah to 0, to make it work but yet I see all the codes setting ah to 0.

Could anyone please explain why I don't have to set ah to 0 and why do everyone do it when its not necessary ??

Thank you.

 

[Wody]

Hello,
The 16-bit AX register contains two 8-bit registers, AH and AL.
By saying 'mov ax, 0x13' you are actually saying 'mox ax,0x0013' which means 'mov ah,0x00', 'mov al,0x13'.
So, you are doing it twice.
The code you write is supposed to be 'mov ah,0x00', 'mov al,0x13', or 'mov ax,0x13'
Wouter Dijkslag

http://www.wody.demon.nl