How do you print a smiley-face in assembly?

Question

I wrote a program in assembler and compiled it. It is meant to print a blue smiley face and then wait for the user to press a key before it terminates. It does do that last bit but it doesn't print the smiley face. Can someone explain what have I done wrong ?

CSEG segment
org 100h
Begin:

mov ax,0B800h
mov es,ax
mov di,0

mov ah,31
mov al,1
mov es:[di],ax

mov ah,10h
int 16h

int 20h

CSEG ends
end Begin

I compiled it with MASM with a 16 bit linker

Answer 1

You can only poke the video buffer directly if you're in a text-only video mode. I'm guessing that you're using Windows of some kind and not actually booting DOS, so you probably are in a graphics mode.

What you may be able to do is open a console window and then AltEnter to go to a full-screen text mode. Try running your program there.

Answer 2

It's been about a year or so since I worked with MASM and the only reference book I have at home is MIPS, so I'm admittedly a bit rusty, however print to screen requires a system interrupt (int 21h), yet the only system interrupt I'm seeing is the program termination call after the keyboard interrupt.

Answer 3

Your code is ok, you just need to either run full-screen as Greg Hewgill suggested, or set up your command window to use an old raster font (like SYSTEM). Right click the title bar of the window and have a look at the Font tab.