COM ports in BIOS

Compaq / E500
March 10, 2009 at 15:26:57
Specs: Windows 98SE, 256k
I have a question for the many of you who know more than I do. My built in infrared device on a Compaq 98SE platform gives an initialization error when run, which I think is not a driver issue. This infrared device is on LPT3 and COM4. LPT3 checks OK. However, ‘mode com4’ in DOS returns an illegal device message AND under debug- COM4 has a value of 00 00. The com address actually used by the Infrared device (3E8) is shown under COM3 instead of COM4 !! COM3 also returns an illegal device message with the mode com3 command. Does this explain my Infrared initialization error?

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March 10, 2009 at 23:24:59
If it's a virtual port, that is one created by software and often used for a winmodem, then I doubt the mode command will work.

If it's a virtual port go into cmos bios setup and make sure neither of the com ports is using that address. If it's a hardware port make sure only your com4 is using that address.

Seems like on some bios' you can select the second com port as an IR port. Is that something you need to do? Or does your IR device connect through a regular com port?

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March 11, 2009 at 14:28:07
The IR port uses COM4. Maybe COM4 is virtual, because it does have 00 00 value in debug and is not recognized by the mode command. But in Modems Properties -> Diagnostics, COM4 displays as having no address or settings, all blank. COM2 is used by the modem, which works. All 4 COM ports are listed in win.ini with default settings shown.

My Compaq bios settings only allow me to enable and disable ports. No other options.

The main issue remains that COM3 shows the address for the Infrared Device, and this port does not open. Whereas the Infrared Device is seeking and using COM4, and I get an initialization error when opening IR on my computer.

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March 11, 2009 at 19:34:51
First, how many physical com ports do you have? The most a PC comes with now is 2. They don't necessarily have to be com1 and com2 but there's usually no reason for that to not be the case.

If you have more than 2 physical ports then I take it you've added a serial card. If that's the case you need to make sure the com ports on the card use different addresses and, if possible, different IRQ's than the on-board ports. Com ports can share IRQ's but it's usually not a good idea.

If you've gone through 'add new hardware' and manually created a com port you need to delete them in device manager. You can't create a virtual port that way, as a virtual port creates its own and won't use a pre existing setting.

If you're unsure about the hardware ports you can just remove them all from device manager (but not the modem's, or any other virtual port). Then let 98 set them up again on next boot.

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