Nasm problem

[sbeng77]

Hi,
i'm trying win32 nasm:

segment code
main:

mov dx,message
mov AH,9
int 0x21
;mov ax,0x4c00
int 0x21
ret
segment data
message db 'test','$'

on dos shell i digit:

nasm -o test.com -f bin test.asm

Now, when i execute this test.com, it print many "strange" characters and also "test" string. Which is error?
Thank you.

[Combuster]

Code: Select all

ORG 100h

[sbeng77]

Ok,
now it's ok.
There's code:

org 100h
message db 'Hello',13,10,'$'

main:

mov dx, message
mov AH,09h
int 21h

I don't understand if i try to replace "Hello" with "test", it give me an error of "CS:...." during executing file.exe/com. Why?

[pcmattman]

Do you update the "mov AH,09h" line?

[sbeng77]

I don't understand.

[pcmattman]

Wait, never mind. I was thinking of the wrong int 21 function - been a while since I've delved into that sort of stuff.

You might want to put the "message db...." line after the code, otherwise it might possibly attempt to execute the string. There's no segments or whatnot in a COM file

[sbeng77]

I permit to extend this thread with another question:

org 100h

mov ax,num1
add ax,num2
aaa
mov dx,ax
mov ah,09h
int 21h
mov ah,4Ch ; ah = 4Ch
int 21h
num1 DW 10
num2 DW 15

I would sum num1 with num2 and print to screen. When executing this code it give me bad characters and not only 25.

[pcmattman]

You need to convert the integer to a string first - at the moment it'll write the ASCII character 25, not 2 and 5.

[Combuster]

Do you know exactly what

Code: Select all

mov ax,num1

does?

[sbeng77]

Insert num1 at ax register

[Combuster]

Insert num1 at ax register

and what is "num1"?

[sbeng77]

Insert num1 at ax register

and what is "num1"?

DW

[Combuster]

That answer would score you zero points on a test for being too obvious, try again.

[sbeng77]

org 100h

mov al,num1
add al,num2

mov dx,ax
mov ah,09h
int 21h
mov ah,4Ch ; ah = 4Ch
int 21h

num1 db 5
num2 db 3


Ok, now i've sum two number but when execute this code it prints me many bad characters!

[AJ]

I think what Combuster was getting at is that you are actually loading ax and dx with pointers.

The second problem is that for DOS interrupts, a quick look in RBIL shows that Int 21h ah = 09h reveals that DS:DX should contain a pointer to a '$' terminated string. You need to convert your numeric answer to a string (once you have learned what [] does) and then add '$' termination, also ensuring that DS points where expected.

Cheers,
Adam