Assembly: troubles with drawing a square

Question

wrote that code in asssembly:

[bits 16]
[org 0x7c00]

mov ah, 0 ;
mov al, 13h ; set graphic mode
int 10h ;

mov cx, sx
mov dx, sy
mov ah, 0ch

colcount:
inc cx
int 10h
cmp cx, hh
jne colcount

mov cx, sx
inc dx
cmp dx, ww
jne colcount

;;; vars section
sx dd 0 ;start x position
sy dd 0 ;start y position
hh dd 30 ;height
ww dd 30 ;width

times 510 - ($ - $) db 0x0
dw 0xaa55

i expected this code to draw a square at the top left corner of the screen but it draw only a rect in the middle.
I don't know where is the problem.
I use nasm as compiler, there aren't any error message.
I took a part of that code from Stackoverflow, thanks YonBruchim.

Answer 1

Try moving the cursor to the right coordinate using the 10h interruption function 2h before drawing

It should look like this

mov ah, 02h
mov dh, 0h
mov dl, 0h
int 10h

Add this code after you set the graphic mode