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Using Debug to Test Hardware

Testing Ports

To test whether the ports on your computer are working, first
1. Type DEBUG (at a DOS prompt).
2. At the hyphen, type D40:00.

Communication Ports

NOTE: The first COM port will usually be in the left most position in the DEBUG list. This is not always COM1. An example of this is when a DB modem is set to COM3, and the R232 serial port is set to COM2, DOS will back fill the active COM ports, so COM2 will show as COM1 to DOS, but its address will still be F802.

You can determine if the ports are active by checking this print out. The port address shows the port is active, 00 00 shows it is not recognised. The example below shows COM1 (F8 03) and COM2 (F8 02) active, COM3 and COM4 inactive:

 COM1COM2COM3COM4 
0040:0000  F8 03F8 0200 0000 00-78 0300 0000 001F 05
0040:0010  61 C4B0 7C02 0001 60-00 002A 002A 0034 05

Parallel Port

You can determine if the port is active by checking this print out. the port address shows the port is active, 00 00 shows it is not recognised. The example below this shows LPT1 (78 03) active.

 LPT1 
0040:0000  F8 03F8 0200 0000 00-78 0300 0000 001F 05
0040:0010  61 C4B0 7C02 0001 60-00 002A 002A 0034 05

Mouse Port

You can determine if the port is active by checking this print out. In the example below, "61 C4" shows it is active.

0040:0000  F8 03F8 0200 0000 00-78 0300 0000 001F 05
 MOUSE 
0040:0010  61 C4B0 7C02 0001 60-00 002A 002A 0034 05

Game Port

Port activity can be determined by:

  • Have a joystick attached to the port
  • Type DEBUG and press Enter
  • At the hyphen type i201
  • You will get FF if no port is found, or F0 or F4 if a port is found
  • Hold the fire button on the joystick. 6. At the hyphen type i201 .
  • Another number will appear. If this number is different than the first number the game port is working.

Debug Routine to Clear the Master Boot Record

Use this routine in the following circumstances, -

  • FDISK does not recognize the hard disk and NO hard disk error messages appear on POST, such as "Fixed disk 0 Failure".
  • There is a virus on the master boot record of the hard drive, and the virus detection program will not clear it.
  • There are non-DOS partitions to be removed.

Warning - This will remove all partitions from the hard disk drive including non-DOS partitions. This will also wipe all the data off the drive.

Create a boot disk with DEBUG, FDISK, FORMAT, and SYS on it. Boot using this disk, then type in DEBUG at the DOS prompt, and you will see a '-' mark. Then type the following, (Press Enter after each line) -

  • FCS:200 400 0
  • RAX
  • 0301
  • RBX
  • 0600
  • RCX
  • 0001
  • RDX
  • 0080
  • E 100 CD 13
  • P
  • Q

You will be back at the DOS prompt. Now run FDISK, then FORMAT.


Debug Routine to Test A Printer

If you cannot figure what is wrong with your printer. Try this out -

Get to an MS-DOS prompt, then type in the following,
Debug
i379

This should return a 2 digit code. If the first digit is anything other than D, then there is something wrong with the printer. The second digit should tell you what the problem is. Use the table below to convert the digit -

1 - 0001...............9 - 1001
2 - 0010...............A - 1010
3 - 0011...............B - 1011
4 - 0100...............C - 1100
5 - 0101...............D - 1101
6 - 0110...............E - 1110
7 - 0111...............F - 1111

The 4 digits tell you the following things,

1 - Printer Selected / Not Selected
2 - Paper Error / No Paper Error
3 - Printer Acknowledged / Not Acknowledged
4 - Not Busy / Busy.

For example the,

DF = 1111 = Selected (1), No Paper Error (1), Acknowledged (1), Not Busy (1).
87 = 0111 = Selected (0), No Paper Error (1), Acknowledged (1), Not Busy (1).

On a HP DJ500C, DF meant the printer was working fine. 87 meant the printer wasn't switched on.


Debug Routine to Indentify a Graphics Card


It is possible to use the DOS program DEBUG to identify which graphics card is in your computer.

From an MS-DOS prompt, type in debug and press the enter key.


At the dash prompt type d C000:0010 and press the enter key.


In the text output you will see the name, though possibly broken up, of your video card.

Here is an example of the debug procedure done on a 9FX Motion 771 with the S3-968 chipset and the 2.05.15 bios revision:

C000:0010  00 00 00 00 00 00 00 00-10 02 00 00 00 00 49 42 
 ..............IB
C000:0020  4D 20 56 47 41 20 43 6F-6D 70 61 74 69 62 6C 65 
 M VGA Compatible
C000:0030  20 42 49 4F 53 2E 20 00-BB 66 F0 01 A3 01 F0 09 
  BIOS. ..f......
C000:0040  09 FF 00 02 4E 75 6D 62-65 72 20 4E 69 6E 65 20 
....Number Nine
C000:0050  56 69 73 75 61 6C 20 54-65 63 68 6E 6F 6C 6F 67 
 Visual Technolog
C000:0060  79 20 20 20 20 20 20 20-20 20 20 39 46 58 20 4D 
 y       9FX M
C000:0070  6F 74 69 6F 6E 20 37 37-31 20 20 20 20 20 20 20 
 otion 771
C000:0080  20 20 20 0E 20 4C 65 74-20 69 74 20 62 65 20 36 
   . Let it be 6

By hitting the d key and then the enter key again at the dash prompt, you will see a continuation of the above output which will identify the chipset (in this case 968) and bios version (shown here as 2.05.15).

C000:0090  38 2E 2E 2E 00 28 63 29-31 39 39 35 20 4E 75 6D   8....(c)1995 Num
C000:00A0  62 65 72 20 4E 69 6E 65-20 56 69 73 75 61 6C 20   
ber Nine Visual
C000:00B0  54 65 63 68 6E 6F 6C 6F-67 79 20 43 6F 72 70 2E   
Technology Corp.
C000:00C0  0D 0A 41 6C 6C 20 52 69-67 68 74 73 20 52 65 73   
..All Rights Res
C000:00D0  65 72 76 65 64 0D 0A 00-23 39 2D 39 36 38 20 42   
erved...#9-968 B
C000:00E0  49 4F 53 20 56 65 72 73-69 6F 6E 20 32 2E 30 35   
IOS Version 2.05
C000:00F0  2E 31 35 0D 0A 00 28 63-29 31 39 39 35 20 53 33   
.15...(c)1995 S3
C000:0100  20 49 6E 63 20 56 65 72-73 69 6F 6E 20 32 2E 30   
Inc Version 2.0

By pressing the q key and then enter, you will exit the debug session and return to the "C:\>" command prompt.



Debug Routine to Clear BIOS Settings

If you would like to clear the BIOS without opening your computer case, then try this -

At the MS-DOS prompt, type the following (pressing enter after each line) -

  • DEBUG
  • o70 16
  • o71 16
  • Q

This will return you back to the DOS prompt. When it does, restart the computer. If it stops at a checksum error, then enter the BIOS, save the default settings, then exit.