Home/ Questions/Q 6616395
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-25T20:34:38+00:00

I’m trying to use the debug tool in windows to for a simple program.

  • 0

I’m trying to use the debug tool in windows to for a simple program. I want to input a string of characters and then inspect the memory to see the characters saved.

Here’s the code I have:

mov  bx,200
mov  byte [bx],33   ;; Set maximum string length (32 + Ent)
mov  ah, 0Ah
int  21h

Every time I assemble the code and run it, it lets me input the string and then DEBUG automatically quits. This my first time ever using it so I’m not sure what the problem is.

Any help/tips would be greatly appreciated.

Thanks!

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Function 0Ah expects the buffer address in DS:DX, your code only sets up BX, never DX.

    Here’s how I type the code in: 

    C:\>debug
-a 100
13DB:0100 mov bx, 200
13DB:0103 mov byte [bx], 33
13DB:0106 mov ah, 0a
13DB:0108 mov dx, bx
13DB:010A int 21
13DB:010C

    Here’s what I get: 

    -u 100
13DB:0100 BB0002        MOV     BX,0200
13DB:0103 C60733        MOV     BYTE PTR [BX],33
13DB:0106 B40A          MOV     AH,0A
13DB:0108 89DA          MOV     DX,BX
13DB:010A CD21          INT     21

    Here’s what’s in the registers:

    -r
AX=0000  BX=0000  CX=0000  DX=0000  SP=FFEE  BP=0000  SI=0000  DI=0000
DS=13DB  ES=13DB  SS=13DB  CS=13DB  IP=0100   NV UP EI PL NZ NA PO NC
13DB:0100 BB0002        MOV     BX,0200

    Next I just use the “proceed” command to execute the code instruction by instruction:

    AX=0000  BX=0000  CX=0000  DX=0000  SP=FFEE  BP=0000  SI=0000  DI=0000
DS=13DB  ES=13DB  SS=13DB  CS=13DB  IP=0100   NV UP EI PL NZ NA PO NC
13DB:0100 BB0002        MOV     BX,0200
-p

AX=0000  BX=0200  CX=0000  DX=0000  SP=FFEE  BP=0000  SI=0000  DI=0000
DS=13DB  ES=13DB  SS=13DB  CS=13DB  IP=0103   NV UP EI PL NZ NA PO NC
13DB:0103 C60733        MOV     BYTE PTR [BX],33                   DS:0200=33
-p

AX=0000  BX=0200  CX=0000  DX=0000  SP=FFEE  BP=0000  SI=0000  DI=0000
DS=13DB  ES=13DB  SS=13DB  CS=13DB  IP=0106   NV UP EI PL NZ NA PO NC
13DB:0106 B40A          MOV     AH,0A
-p

AX=0A00  BX=0200  CX=0000  DX=0000  SP=FFEE  BP=0000  SI=0000  DI=0000
DS=13DB  ES=13DB  SS=13DB  CS=13DB  IP=0108   NV UP EI PL NZ NA PO NC
13DB:0108 89DA          MOV     DX,BX
-p

AX=0A00  BX=0200  CX=0000  DX=0200  SP=FFEE  BP=0000  SI=0000  DI=0000
DS=13DB  ES=13DB  SS=13DB  CS=13DB  IP=010A   NV UP EI PL NZ NA PO NC
13DB:010A CD21          INT     21
-p

    Then type in “QWE” followed by enter:

    QWE
AX=0A0D  BX=0200  CX=0000  DX=0200  SP=FFEE  BP=0000  SI=0000  DI=0000
DS=13DB  ES=13DB  SS=13DB  CS=13DB  IP=010C   NV UP EI PL NZ NA PO NC
13DB:010C 0000          ADD     [BX+SI],AL                         DS:0200=33
-

    Done. And here it is in the memory:

    -d 200
13DB:0200  33 03 51 57 45 0D 00 00-00 00 00 00 00 00 00 00   3.QWE...........
13DB:0210  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00   ................
13DB:0220  00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00   ................
    • 0