NiTiN wrote:
> Hi!
>
> I've got some really simple code that boots the system and displays a
> string. I've looked at a couple of examples and I'm aware of the load
> to 0x7c00. My jump references are fine but when I try to access
> variables, I get nulls instead of the actual data.
>
> Here's the source code:
> bits 16
> org 0x7c00
>
> jmp start
>
> helloMsg db 'A'
>
> start:
xor ax, ax
mov ds, ax
> mov al, [helloMsg] ;copy the A
> cmp al, 65
> jne wrongChar
>
> call printChar ;print the A
> jmp end
>
> wrongChar:
> mov al, 66 ;print B if wrong character
> call printChar
>
> end:
> jmp $
>
> printChar:
> mov ah, 0eh
> ;mov al, 65
> mov bh, 0h
> mov bl, 7h
> int 10h
> ret
>
> ;510 bytes plus the 2 byte signature
> zero_padding: times 510 - ($ - $$) db 0
>
> ;boot signature
> boot_sig: dw 0xaa55
>
>
> The output I get on running this code is 'B' when it should be 'A'. I
> must be missing something.
ASSume nothing, except that your code is loaded at 7C00h, and the boot
drive is in dl. Might want to think about where your stack is, too...
Best,
Frank
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