DOS and ntvdm differences

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bMind

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

bMind 01 Jul 2006, 15:22

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: 8356
Location: Kraków, Poland

Tomasz Grysztar 01 Jul 2006, 15:58

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 02 Jul 2006, 01:48

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 02 Jul 2006, 08:50

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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