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:

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.

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.

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 -

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.

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.