Assembly question

[geek@02]

Hi i'm trying to compile this newbies' asm prog on nasm16. but i get 'invalied combination of opcode and operands' error on line 18: mov es:[bx], ah. Could anyone point out the reason please?

[BITS 16]
[ORG 0100H]

[SECTION .text]

START:    

mov ax, 0003h
int 10h

mov bx, 0b800h
mov es, bx

mov bx,0
mov ah, 1
mov es:[bx], ah

mov ax, 0100h
int 21h

mov ax, 4c00h
int 21h

[SECTION .data]

thx.

[matsp]

You will need to change your code to have:

mov [es:bx], ah

or

es mov [bx], ah

or

es
mov [bx], ah

See http://nasm.sourceforge.net/doc/nasm...ml#section-3.1

--
Mats

[geek@02]

That worked. Thanx Mats.

[VirtualAce]

Plotting pixels in B800 video eh. Why are you specifying this is a COM file?

[brewbuck]

Plotting pixels in B800 video eh. Why are you specifying this is a COM file?

org 100h doesn't necessarily mean a COM file. An EXE could have its origin there as well, although I'm not sure why you'd do that.

[geek@02]

i picked up the org 100h thing from a book. Here's the books' explanation for it: "The real mode flat model has a 256-byte prefix at the beginning of its single segment. This is the Program Segment Prefix (PSP) and it has several uses that I won't be explaining here. The PSP is basically a data buffer and contains no code. The code cannot begin until after the PSP, so the 0100H value is there to tell DOS to skip those first 256 bytes."

Though the prog works fine when i remove the org 100h line.

[matsp]

i picked up the org 100h thing from a book. Here's the books' explanation for it: "The real mode flat model has a 256-byte prefix at the beginning of its single segment. This is the Program Segment Prefix (PSP) and it has several uses that I won't be explaining here. The PSP is basically a data buffer and contains no code. The code cannot begin until after the PSP, so the 0100H value is there to tell DOS to skip those first 256 bytes."

Though the prog works fine when i remove the org 100h line.

That is because the "space for PSP" is only needed for .COM applications, not for .EXE applications.

--
Mats

[geek@02]

i just assembled it into a COM file without the org line -- still it works.

[matsp]

i just assembled it into a COM file without the org line -- still it works.

Probably because nasm automagically adds a org 100h anyways [or something to that extent].

--
Mats