DOS and ntvdm differences

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bMind

Joined: 01 Jul 2006
Posts: 2
Location: Russia,Zheleznogorsk

bMind

I code DOS application and write to [es:di] word correctly.
It works in DOS but in ntvdm does not.
Why it happens? How to solve it?

Code:

org 100h
use16

@@:
mov ax,0B800h
mov es,ax

mov ah,7       ;set attribute
mov si,mess1
xor di,di
cld

@@:
lodsb

cmp al,'$'
jz .done

mov [es:di],ax
add di,2
jmp @b

.done:
mov ah,10h
int 16h

int 20h

mess1 db "Press ANYKEY please$"

01 Jul 2006, 15:22

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 7861
Location: Kraków, Poland

Tomasz Grysztar

Interesting, video memory seems to be somehow inactive at startup under NTVDM, however it gets activated if you call the INT 10h somehow, for example adding this simple check:

Code:

mov ah,0Fh
int 10h
cmp al,3
jne no_text_mode

(which anyway is recommended when you do such access like above) at the beginning makes it work.

01 Jul 2006, 15:58

bMind

Joined: 01 Jul 2006
Posts: 2
Location: Russia,Zheleznogorsk

bMind

Thank you, Tomasz. It works.

PS:close this topic please, I don't found how.

02 Jul 2006, 01:48

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid

Tomasz: i think it's quite logical behavior... for easier running of apps that doesn't make any output to screen

02 Jul 2006, 08:50

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