assembly - Memory-Mapped Graphics Output -

i'm exploring drawing pixels , lines, using memory-mapped graphics. i'm using tasm in textpad, in windows. when click run whole screen turns blue , that's it, no pixels drawn.

.model small .stack .data    savemode db ? xval dw ? yval dw ?  .code main proc mov ax, @data mov ds, ax  call setvideomode call setscreenbackground         call draw_some_pixels call restorevideomode   mov ax, 4c00h int 21h main endp  setscreenbackground proc     mov dx, 3c8h     mov al, 0     out dx, al      mov dx, 3c9h     mov al, 0     out dx, al      mov al, 0     out dx, al     mov al, 35     out dx, al     ret setscreenbackground endp   setvideomode proc     mov ah, 0fh     int 10h     mov savemode, al      mov ah, 0     mov al, 13h     int 10h      push 0a00h     pop es     ret setvideomode endp  restorevideomode proc     mov ah, 10h     int 16h      mov ah, 0     mov al, savemode     int 10h     ret restorevideomode endp  draw_some_pixels proc     mov dx, 3c8h     mov al, 1     out dx, al      mov dx, 3c9h     mov al, 63     out dx, al     mov al, 63     out dx, al     mov al, 63     out dx, al      mov xval, 160     mov yval, 100      mov ax, 320     mul yval     add ax, xval      mov cx, 10     mov di, ax      dp1:         mov byte ptr es:[di], 1          add di, 5     loop dp1     ret  draw_some_pixels endp 

the issue seems segment video mode 13h associated with.

after setting video mode, next step draw onto screen. vga memory located @ physical address 0xa0000

your code does:

setvideomode proc     mov ah, 0fh     int 10h     mov savemode, al      mov ah, 0     mov al, 13h             ; video mode 13h     int 10h      push 0a00h              ; incorrect should 0a000h     pop es     ret setvideomode endp 

video mode 13h addressed segment:offset (es:0 in case) of 0a000h:0. 0a000h:0 physical address (0a000h << 4) + 0 = 0a0000h.

the code fixed changing to:

    push 0a000h     pop es