Hello I'm trying to clear the screen in DOS video mode with this code.
But when I run it, the dot is still there!
org 100h
mov ah, 0 ; set display mode function.
mov al, 13h ; mode 13h = 640x480 pixels, 256 colors.
int 10h ; set it!
mov cx, 10 ; column
mov dx, 10 ; row
mov al, 15 ; white
mov ah, 0ch ; put pixel
int 10h ; draw pixel
; ------- clear the screen ----------
; ------- doesn't work! dot is still there
mov ax,0B800h
mov es,ax
xor di,di
xor ax,ax
mov cx,2000d
cld
rep stosw
; -------------------------------------
;wait for keypress
mov ah,00
int 16h
mov ax, 4c00h ; exit to operating system.
int 21h
;======================================================
I tried resetting the video mode with INT 10 but this gives me blinks which is unwanted inside my loop
There are some issues with your code.
First, BIOS mode 13h is not 640x480 at 8 bits/pixel, it's 320x200 at 8 bits/pixel.
B800h is the address of BIOS text modes. BIOS graphics modes use A000h.
So it should be:
mov ax,0A000h
mov es,ax
xor di, di ; ES:0 is the start of the framebuffer
320x200 at 8 bits consumes 320*200 = 64 000 bytes of video memory. So the value of cx is incorrect. It should be:
mov cx,32000d ; you can write 320 * 200/2 in your source if you want
cld
xor ax,ax
rep stosw ; zero 2*CX bytes at ES:DI