This works anywhere outside of DOSbox

msdos pc or what?

Windows XP, I don't have a DOS pc to try it on. DOSbox is the only thing that I have found that this error occurs on. I'll take a screenshot if that helps.

xp!=dos

I know, but this is 16-bit assembly, I see no reason that it should not work in DOS.

I see no reason that it should not work in DOS.

Uhm yeah so either do that (and subsequently write a mail to microsoft why
their gfx emulation is screwed) or stop complaining about unverified bugs.

Okay, thanks for the replies. I honestly didn't mean to offend you or upset you, sorry for that.

Usually testing it against bochs (elpin bios) or some virtualizer (vmware, vpc, virtualbox)
with installed msdos or freedos gives you a way better impression of what may actually
be right and what not (in case you don't "believe" dosbox).
Btw. you can turn off the blinking using an int10 call (al=3, bl=0/1).

My assembly is extremely rusty so I may be completely off base here, but it looks like the problem is you aren't setting the video mode to one capable of 256 colors. On a real dos machine (and DOSBox) by default you'll have a 16 color text mode, so once you go past the first 16 colors you'll run into odd stuff like the same colors only flashing, etc. I believe a dos prompt in XP behaves differently. I think to get this working you would have to explicitly set to something capable of 256 colors by first doing something like:
mov ah, 0
mov al, 13
int 10h

I think the OP meant 256 text color attributes, and wanted to see intense background colors rather than blinking text. The high bit of the attribute can mean either blinking or intense background depending on a bit in one of the video registers, and the BIOS call wd pointed out can toggle it.

Confirmed that enabling background intensity allows use of 256 color attributes, thank you sir.

1[org 0100h]
2
3
4[section .text]
5	mov ax,1003h
6	mov bl,0
7	mov bh,0
8	int 10h
9
10	mov bl,01
11
12MAIN:
13	cmp word [counter],255
14	je DONE
15	cmp byte [keep_neat],16
16	je ENDLINE
17	mov cx,1
18	mov al,0
19	mov ah,9
20	int 10h
21	mov dx,blank
22	call WRITE
23	inc bl
24	inc byte [keep_neat]
25	inc word [counter]
26	jmp MAIN
27
28DONE:
29	mov ah,4ch
30	mov al,0
31	int 21h
32
33WRITE:
34	mov ah,9
35	int 21h
36	ret
37
38ENDLINE:
39	mov dx,eol
40	call WRITE
41	mov byte [keep_neat],0
42	jmp MAIN
43
44
45
46[section .data]
47counter dw 0
48blank db "0", "$"
49keep_neat db 0
50eol db 13, 10, "$"

But these are only 16 colors 😉

ripsaw8080 wrote:

I think the OP meant 256 text color attributes, and wanted to see intense background colors rather than blinking text. The high bit of the attribute can mean either blinking or intense background depending on a bit in one of the video registers, and the BIOS call wd pointed out can toggle it.

Ah, that makes a lot more sense then 😀