The purpose of this experiment is to introduce you to a powerful 80x86 assembly/machine language utility called DEBUG.

Preparing Your DEBUG Environment

If you have an older version of Windows (95, or 98) or Windows XP 32-bit, or Windows Vista 32-bit, or Windows 7 32-bit, then the DEBUG utility program is built into the operating system. You can prove this to yourself by opening a Command Prompt window (Start, Run, type debug into the run field, and click OK, or just click the Command Prompt icon). Once inside the Command Prompt window, type debug and press Enter. If you get an error then DEBUG does not exist on your Windows system.

Start Menu showing Command Prompt icon

If you have 64-bit versions of Windows XP, Vista, 7, or 8, then you need to install some special software to create a DEBUG environment.

The special software you need (DosBox) as well as the actual DEBUG program are saved in the following ZIP file:

The debughelp2.doc document explains how to unzip the files and get DEBUG running through DosBox.

Procedure

1. Read Appendix D, pages 560 through 575. Perform all the example DEBUG command exercises that are presented.

2. Here is the DEBUG program you need to enter and execute:

a
mov ax,0
mov bx,1234
mov cx,5678
mov dx,9abc
and ax,bx
or ax,cx
xor ax,dx
not ax
r
t 8
q

3. Run DEBUG and enter the program and commands line by line. The blank line after the not ax instruction is needed to get out of the "a" command.

4. Examine the DEBUG output. The final value in AX should be 333B. This would be a good time to do an Alt Print Screen to capture a screen shot of the DEBUG window to paste into your lab writeup.

5. Quit DEBUG and then run it again.

6. After entering the "a" command, change the first instruction from

mov ax,0

to

mov ax,????

where ???? is your 4-digit birth date. For example, if you were born on July 15, your instruction would be mov ax,0715

Then enter the rest of the instructions and commands.

7. Use DEBUG to run the modified program. Do another Alt Print Screen to grab the new DEBUG results for your lab writeup.