I recently purchased and installed a SuperMicro P55T2S motherboard
with an AMI BIOS dated 7/15/95 (coded S6Y0T8 or something like that) into my
system. This board comes with two 16550 onboard serial ports.
I use an internal Zoom modem on COM2 and my mouse on COM1 so I used
the BIOS to disable the second COM port in the 'Peripherals' section of the
CMOS settings. I also reserved IRQ4 for the ISA/EISA bus in the PCI interrupt
Whenever I boot, the BIOS summary screen shows the existence of two COM
ports at their expected port addresses. Also, OS/2 boots without any error
messages about the lack of a need for COM.SYS and VCOM.SYS so I assume
the system sees the second port correctly - remember the first is actually
the mouse. Tests using MSD or PC-DOS's QCONFIG indicate the existence of
two serial ports at the expected standard configuration parameters.
The problem is that about 75% of the time when I try to access the modem,
either through the Internet dialer, FaxWorks, or any terminal program, it does
not respond. There is no 'OK' message or any other message for that matter.
Note that the other 25% of the time, the modem seems to work and I'm not just
talking about 1/4 of the time when I reboot. If I try to use the modem 10 times,
only about 2 of those times will I get responses from the modem.
When I boot into DOS, the modem is always accessible to my comm programs so
its definitely something with OS/2. I immediately assumed an IRQ conflict but the
modem is jumpered for the standard IRQ3 needed for COM2 (or is it IRQ4 for COM2
and IRQ3 for COM1? Anyway, the card is setup correctly for COM2 whether or not
my mind remembers the IRQ correctly right now.) However, checking the CMOS
settings and jumpers on the card shows that the MB COM2 is indeed disabled and
that the card is set for COM2. Nothing else in the system should be using COM2 as
far as I can tell.
Anyone have any ideas? Does the modem use DMA channels?
SuperMicro P55T2S w/ AMI BIOS 7/15/95
QLogic Fast SCSI PCI Basic (reports using IRQ10)
Matrox MGA-MIL/2N PCI video card (IRQ? not needed as far as I know)
GVC 2003BT ISA LAN adapter (at IRQ 12)
ProAudio Spectrum 16 ISA (at default OS/2 settings of IRQ7)
Zoom v.34 ISA modem (at IRQ3 and COM2)