Basic Input assembly Language

Question

Hey I have started learning assembly language.

I wrote the following code:

.MODEL SMALL
.STACK 1000H
.DATA
MSG db "Hey$"
.CODE
MAIN PROC
    MOV AX, @DATA
    MOV DS, AX

    MOV AH,0AH ; setting the sub function
    MOV DX, offset msg ; moving address of msg to dx
    INT 21h     ; calling interrupt

    MOV AH, 09
    MOV DX, OFFSET MSG
    INT 21h     ; for printing

    MOV AH, 04Ch    ; Select exit function
    MOV AL, 00  ; Return 0
    INT 21h     ; Call Interupt to Terminate program
MAIN ENDP
END MAIN

I am trying to take input, it is working kind of but when I try printing it I do not get the proper string. I used this list to select the interrupt function.

I am attaching a screenshot, I have given input the following string:

Hey this is me taking input

But I got unexpected result.

Screenshot:

Questions:

• What am I doing wrong here?
• Is there a nice debugger to use when writing assembly programs?
• Any links to good assembly tutorials would be very nice?

Thanks.

Answer 1

http://www.skynet.ie/~darkstar/assembler/intlist.html

Note: With "db Size dup (0)" we can occupy the value of Size amount of bytes.

.MODEL SMALL
.STACK 10H
Size = 3
.DATA
M1  db Size           ; First character=max length
M2  db ?              ; Second char of buffer=length of input
MSG db Size dup (20H) ; Rest of buffer=input string
    db 0DH            ; followed by carriage return (0Dh)
;---
    db "$"            ; (allways needed for printing function)
.CODE
MAIN PROC
MOV AX, @DATA
MOV DS, AX

MOV AH,0AH        ; setting the sub function
MOV DX, offset M1 ; moving address of input buffer
INT 21h           ; calling interrupt

MOV AH, 09
MOV DX, OFFSET MSG
INT 21h           ; for printing

MOV AH, 04CH      ; Select exit function
MOV AL, 00        ; Return 0
INT 21h           ; Call Interupt to Terminate program
MAIN ENDP
END MAIN

Answer 2

You didn't set aside enough space for your input string; when you "declared" MSG, you gave it room for only 4 characters ("Hey$").