🚀 go-pugleaf

  "TK - TBD" <PISS_OFF_SPAMMERS_Thomas_Kjoernes@phoenix.com> wrote:
> tunney <bigmacmeal@hotmail.com> wrote in article
> <7c6u0d$cue$1@winter.news.rcn.net>...
> > I know that this is a thick question, but could someone explain to me
> > how to clear the screen in text and video mode, can't for the life of me
> > figure out how. Please help me I have an exam in this soon.
> > Also could someone explain int 21h service 0Ah
> >
> > Thanks a million.
>
> Clearing the screen (TEXTMODE) is easy:
>
> mov ax, 3	; set mode 3, voil� screen is cleared.
> int 10h		;
>
> For less flickering... you could clear it by filling video mem
> directly, like this:
>
> push 0B800h
> pop es
> xor ax, ax
> xor di, di
> mov cx, 16384
> rep stosw
>
> For video mode, ask someone else.

I think it should be "graphics" mode, not "video" mode. It's not a lot harder.
For CGA graphics modes the above will also work. For chained modes (MCGA 13h)
you clear 64k starting at 0A0000h:

clear_a0000:
mov ax, 0A000h
mov es, ax
sub ax, ax
sub di, di
mov cx, 32768
cld
rep stosw

For non-chained modes the above clears only bit plane selected in sequencer.
To clear screen you need to allow write to all 4 bit planes:

mov dx, 3c4h
mov ax, 0F02h
out dx, ax

Of course, it's a good idea to save previous bit plane write bitmask and later
restore it.

Save (in BL):
mov dx, 3c4h
mov al, 2
out dx, al
inc dx
in al, dx
mov bl, al

; Here allow write to all bitplanes and clear memory.

Restore (from BL):
mov dx, 3c4h
mov al, 2
mov ah, bl
out dx, ax

That's all for standard VGA BIOS modes. I hope that you don't need to deal
with non-standard modes ('X' or how is it called now?) - it's no harder just
more dirty work.


-- Sclerosis cannot be healed but can be forgotten --

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