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PC Hardware - Peripheral Issue

Why won't my computer recognize any COM ports? by topscribe
Posted: 30 Dec 01

In Windows, go to Start > Settings > Control Panel. Double-click the "Add New Hardware" icon. Allow Windows to search for new hardware by itself. Chances are, it will find the ports and add them for you.

If it doesn't find them, go into CMOS. Your computer will usually tell you which key(s) to press for this, when it first starts booting up. You should be able to find something in there to the effect of peripheral configuration, where you can see whether the ports have been enabled or disabled. Of course, you want them enabled.

If they show enabled, you can next see if I/O addresses have been assigned to the serial (COM) ports by booting into DOS mode. (You can do that two ways: [1] hitting the <F8> key just as you hear the beep when it is booting up or [2] choosing "Shut Down" in Windows then "Restart in MS-DOS mode.") Once in DOS, type


You will see nothing but a hyphen, but this is as it should be. This is when you will type

D 40:00 09

If the serial ports are present, you will likely see a line that looks something like this (but not exactly, necessarily, depending on how many ports it recognizes--up to four):

0040:0000 F8 03 F8 02 00 00 00 00-78 03

If there are no serial ports, it will look like this:

0040:0000 00 00 00 00 00 00 00 00-78 03

To get out of the Debug program, by the way, press the <Q> key, then <ENTER>.

If you still get nothing, you may have a bad controller. In this case (assuming it is an onboard controller, as most are now), you may need to purchase a UART expansion card and connect your serial ports to that (about $40 downtown). If this is your recourse, by the way, you may need to go back into CMOS and disable everything you are replacing since that could interfere with the performance of the UART card, even though it did not recognize the ports in the first place. The card, by the way, will also have an accomodation for a parallel port, which you may now need to use, whether or not the onboard one works, if keeping the onboard one enabled is confusing the computer.

NOTE: If your PS2 port for your mouse also won't work, you can get an adapter to convert your mouse from PS2 to serial. It's just a little gizmo you attach at the end of the cable so you can hook it to either COM1 or COM2 on the UART card, in which case Windows should immediately recognize it as a serial mouse and assign a driver to it. The only problem here is, of course, that the mouse will tie up one of the serial ports. But you will still have one left for an external modem or whatever.

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