Computer debug routines
Disclaimer: The below debug routines are listed to help test and view extended information on your computer. However, some of these debug routines can also damage computer components or cause them not to work properly. We are providing these debug routines as a reference. If these cause problems with the computer they are run on, Computer Hope will not be held responsible for your actions. We recommend that only experienced computer users run these commands and that you are fully aware of the potential hazards of using these routines.
Debug is an MS-DOS command that can be used to enter machine language into the computer either to create programs or test computer peripherals by receiving back various computer machine code.
Note: Newer versions of Windows no longer include the debug command.
Several of the debug routines listed within this page as well as other of our pages return responses in hexadecimal format. It is recommended if you want to understand some of the code in these routines that you get a familiarity of hexadecimal. You can find information about hexadecimal as well as binary on our binary and hexadecimal page.
If during the time you are typing the debug routine you receive ^error, this is an indication that you have incorrectly typed something in the line just completed. You can type the line again without causing any problems with the routine.
Debug has been included in every version of MS-DOS as well as Windows up to Windows XP. When running any of the debug routines, it is recommended that if you have Windows that you exit or shut down to get into a real DOS prompt.
Once at the MS-DOS prompt, run through the example below, this example is perfectly fine to run on any computer running MS-DOS and Windows and will not harm anything.
Type debug and press Enter.
At the debug prompt, - (small dash) type d40:00 and to get several lines of information.
(See Testing Ports for an explanation of this feedback.)
To exit out of debug type q and press Enter to get back to the MS-DOS prompt.
In some of the below debug routines, you will notice that a g is typed, then q. G tells the computer that the code type is not self-executing and must be run at this point. If completed, the program returns "Program Terminated Normally," which indicates you can now quit from the debug program.
Listing of routines
The below debug routine will check the ports of the computer to allow you to know if ports are being detected or not.
Type debug to get to the "-"
You should get several lines; however, the first line is the only important line, which should read the following:
0040:0000 F8 03 F8 02 E8 03 E8 02 - 78 03 78 02 BC 03
|F8 03||F8 02||E8 03||E8 02||78 03||78 02||BC 03|
The above table shows you what the feedback means as far as a port, so if you see F8 03, this would be an indication that COM1 is being detected. If you see 00 00, this is an indication that it is not being detected, which could mean that hardware is bad or that it is disabled in CMOS.
Once you have finished looking at the information, type Q and press Enter to get out of debug.
The below debug routine will clear CMOS, BIOS, passwords, settings, viruses, and other items residing in the CMOS. During this process, you may get returned characters that are an indication that the string has been entered. If you get an ERROR, make sure you have typed the line incorrectly and that no lines have been skipped.
After typing debug, you will get "-" which is where you can begin by typing A and pressing Enter.
MOV AX,0 <Enter>
MOV AX,CX <Enter>
OUT 70,AL <Enter>
MOV AX,0 <Enter>
OUT 71,AL <Enter>
INC CX <Enter>
CMP CX,100 <Enter>
JB 103 <Enter>
INT 20 <Enter>
<Enter> Note: Nothing is typed on this line
G <Enter> When you press G the above script executes, make sure you have read and agree to the above disclaimer.Q <Enter>
Then reboot, and you will get a Setup Checksum Error. Go into setup, correct all the incorrect values, time, date.
The joystick debug test will detect if a joystick is present or not.
Type debug from the DOS prompt once at the -.
If you get an FF response, hold one of the main buttons on your joystick, and while holding the button down type i201 and see if a different response is given. Each button on the joystick should return a different response.
Note: Joysticks with more than 4 to 5 buttons may not return a response for all extra buttons because these buttons are controlled through software.
If an FF is still given on each of the buttons on the game paddle or joystick, it is a good possibility that either the joystick or the joystick port is bad. If possible, attempt these steps with another known working joystick.
However, if you are receiving different responses when pressing and holding the keys on the joystick, the computer hardware is working properly.
Type q and press Enter to quit out of debug.
Extra Note: Computer Hope has experienced issues where this debug routine may not work under Windows NT. If you are currently running Windows NT, refer to our page for joystick installation procedures.
- See joystick help page for additional help with computer joysticks.
Erasing sector two
Before doing the below routine ensure that you have read our disclaimer and that you're sure that this is safe to do on your hard drive. Some computer hard drive manufacturers may void your warranty if this routine is ran or in some situations, this can cause damage to the hard drive. Erasing sector two is useful in clearing DDO and unknown partitions. If this routine completes successfully, it will erase everything in sector two.
In the below debug routine, only type what is in bold from line 3 to 9, you will get a response if typed in properly. If you get a response continue to type the bold text as shown below in the example below.
-FCS:200 400 0<Enter> -ACS:100<Enter> -xxxx:0100 mov ax,302<Enter> -xxxx:0103 mov bx,200<Enter> -xxxx:0106 mov cx,2<Enter> -xxxx:0109 mov dx, 80<Enter> -xxxx:010a int 13<Enter> -xxxx:010c int 20<Enter> -xxxx:0110 <Enter>(without typing anything) -g <Enter> Program terminated normally. -q <Enter>
Erase all hard drive information
Using a debug routine to erase the hard drive partition information is only recommended for experienced users or users who are unable to delete the partition information through fdisk.
In the below debug routine, only type what is in bold from line 3 to 8, you will get a response if typed in properly. If you get a response continue to type the bold text as shown below in the example below.
A:\>debug <Enter> -F 200 L1000 0 <Enter> -A CS:100 <Enter> xxxx:0100 MOV AX,301 <Enter> xxxx:0103 MOV BX,200 <Enter> xxxx:0106 MOV CX,1 <Enter> xxxx:0109 MOV DX,80 <Enter>
(80 for hd 0 or 81 for hd 1 )
xxxx:010C INT 13 <Enter> xxxx:010E INT 20 <Enter> xxxx:0110 <Enter> -g <Enter> Program terminated normally -q<Enter>
Once this debug routine is complete, reboot computer and all partitions should be erased. Before anything can be installed back onto the computer, you must run fdisk and recreate the partition as well as format the hard drive.
- Additional information about fdisk is on our fdisk page.
- Additional information about format is on our format page.
Erase hard drive and clear CMOS
Before doing the below routine ensure that you read our disclaimer as well as are sure that this is safe to do on your hard drive. Some computer hard drive manufacturers may void your warranty or this may cause damage to the hard drive when doing the example below. If this routine completes successfully, it will erase everything from your hard drive as well as your reset your CMOS values.
In the below debug routine, only type what is in bold from line 3 to 17, you will get a response if typed in properly. If you get a response continue to type the bold text as shown below in the example below.
A:\>debug <Enter> -fcs:200 400 0 <Enter> -acs:100 <Enter> -xxxx:010 0mov ax, 0 <Enter> -xxxx:0103 mov ax, cx <Enter> -xxxx:0105 out 70, al <Enter> -xxxx:0107 mov ax, 0 <Enter> -xxxx:010a out 71,al <Enter> -xxxx:010c inc cx <Enter> -xxxx:010d cmp cx,100 <Enter> -xxxx:0111 jb 103 <Enter> -xxxx:0113 mov ax,302 <Enter> -xxxx:0116 mov bx,200 <Enter> -xxxx:0119 mov cx,1 <Enter> -xxxx:011c mov dx,80 <Enter> -xxxx:011f int 13 <Enter> -xxxx:012l int 20 <Enter> -xxxx:0123 <Enter> (without typing anything.) -g <Enter> program terminated normally
If you are doing this debug routine to clear out a possible virus turn off your computer and wait and turn back on.
Once back at DOS, reboot your computer
When your computer comes back on from doing the above, you will get an error message as booting up the computer, such as Invalid Configuration. You must enter CMOS and set the time and date, save, and reboot again. Once rebooted, you will then need to run fdisk and recreate the partitions. Once created, you will then need to format the hard drive and proceed as normal.
Discharge old laptop batteries
The below debug routine is used for older laptop batteries (i.e. batteries made from 1990-1992), we do not recommend using this routine on any newer laptop batteries or any NiMH batteries.
N DPDISCHG.COM <Enter> A <Enter> MOV DX,01E8 <Enter> MOV AL,F9 <Enter> OUT DX,AL <Enter> INT 20 <Enter> <Enter> RCX <Enter> 10 <Enter> W <Enter> Q <Enter>
The above script will write dpdischg.com to the current directory. To run this utility type dpdischg.
Reboot your computer
Implement this debug routine to reboot your computer.
E 40:72 34 12 RCS FFFF RIP 0000 G
To create a batch file that reboots your computer without having to type the above command each time, use the example below.
GOTO BEGIN E 40:72 34 12 RCS FFFF RIP 0000 G :BEGIN DEBUG < REBOOT.BAT
Create a sleep file
Note: The below debug routine has also been made as a file and made available on our utility downloads page.
You should get a "-" begin typing the below information; after each line you may get a response, do not press Enter and type the next line after the response.
N SLEEP.COM A 100 MOV SI,0082 MOV AX,[SI] XCHG AH,AL XOR AX,3030 MOV BL,AL MOV AL,0A MUL AH ADD AX,BX MOV SI,AX MOV AH,2C INT 21 MOV BL,DH MOV AX,SI AAM OR AX,3030 XCHG AH,AL MOV ,AX MOV AH,09 MOV DX,0160 INT 21 MOV AH,06 MOV DL,FF INT 21 JZ 014C OR AL,AL JNZ 013F MOV AH,08 INT 21 MOV AL,FF MOV DX,016C PUSH AX MOV AH,09 INT 21 POP AX MOV AH,4C INT 21 MOV AH,2C INT 21 CMP BL,DH JZ 012D MOV BL,DH DEC SI JNZ 011A SUB AL,AL MOV DX,016C JMP 0142 DB "XX SECONDS", D, 24 DB " ", D, A, 24 RCX 79 W Q
Tip: You may cut and paste the above test into a notepad document and save the file with a .scr extension. Once saved from DOS, type: debug < name of scr that should create SLEEP.COM.
Check BIOS date
The below debug routine is to check the date of your BIOS. All BIOS dates on PC compatible computers is stored at memory address FFFF5h. To display the date of your BIOS do the following:
At the C:\> Type debug
- d FFFF:5 L 8
After typing the above command, you should receive a string similar to:
FFFF:0000 30 34 2F-33 30 2F 39 38 4/30/98
Where 4/30/98 is the current date as set in your computer BIOS.
Additional information about the computer BIOS is on our BIOS help page.
Video card type
At the C:\> Type debug
After typing the above command, you should receive several lines of text similar to:
|C000:0070||00||5B||53||54||42||20||6E||56||-||49||44||49||41||20||54||4E||54||.[STB nVIDIA TNT|
|C000:0080||20||76||65||72||2E||20||31||2E||-||31||30||20||0D||0A||00||1B||43||ver. 1.10 ....C|
|C000:00A0||53||54||42||20||53||79||73||74||-||65||6D||73||20||49||6E||63||0D||STB Systems Inc.|
As you can pick out in the above dump, this gives you enough information to determine the make and the year made on the video card. In line 4 you can see the make of this video card, which in this case is a NVIDIA TNT, which would be the Riva TNT chipset. The next line you notice the version of the card and finally the line after that is the Copyright or the year manufactured.
If you do not see any information that sounds like a video card, you can also type the following command.
The above line gives you a dump similar to the above example; however, it may have additional information about the video card. Additional information about computer video cards is on our video card help page.
- See our debug command page for further information and help on the command.