Misbehaving modems are driving me nuts

Charles Lavin
07-10-2005, 01:58 AM
Hi --

I have two Pentium III machines on Intel 810-based motherboards (one is
Intel's, one is Biostar's) exhibiting this behavior. All PCs here are
running Windows XP Pro SP2.

All the PCs have two built-in COM ports. I have two identical Multitech
external modems connected to these COM ports. These modems, along with the
voicemail application that uses them, were moved from another Pentium III PC
where we were running this application.

When everything is first powered up, the modems have just their power
indicators lit. Just before Windows displays the login screen, both modems
momentarily flash most of the lights on their front panels (I guess that's
when the COM port drivers are being loaded and initialized). But while the
on COM1 returns to having just its power light on, the modem on COM2 keeps
the TD and RD indicators lit as well. These indicators will remain lit as
long as Windows is running.

The modem diagnostics in the modems' properties windows show that the modems
are responding (although it does take longer for the modem on COM2 to
respond). And I can have a conversation with either modem via HyperTerminal.
But the voicemail app that drives the modems doesn't like the modem with the
TD/RD lights on -- it claims the modem is in use and will not initialize it.

I have tried four different serial cables, and I have swapped modems between
the COM ports. It is always the modem plugged into COM2 that behaves this

If I boot the PC to DOS instead of Windows, the problem doesn't happen --
both modems just keep their PWR lights on.

If I boot the PC to Safe Mode or to an XP Safe Mode Command Prompt, the
modems also remain with just their PWR lights on.

I've also tried connecting the modems to an Athlon XP 1800+ (I think)
machine built on an MSI board with an nVIDIA chipset. The problem does not
occur on this PC. After Windows fully boots, the modems stay with just their
PWR lights on until they are initialized by the voicemail app (or

The original PC where this voicemail app was running was a Pentium III PC
running on a board with a VIA chipset. The modems worked fine there, too.
Unfortunately, that PC isn't functional anymore.

I need to get this to work properly on one of the remaining Pentium III
boxes, because I have an ancillary app that requires an ISA card, and the
Pentium III boxes are the only ones with ISA slots.

Right now, I'm leaning toward using the PC with the Intel board (SE440BX-2).
That board's BIOS allows me full control of all COM ports settings. The BIOS
is set up for COM1 at 3F8/IRQ4, COM2 normal (no IR) at 2F8/IRQ3, PnP BIOS
set to NO. Windows reports no conflicts or sharing issues with any of these
addresses or IRQs.

The modems always start out OK, while the PCs go through BIOS POST. It isn't
until Windows has almost fully loaded (at least to the point of displaying
the login screen) that I start to have a problem.

The problem happened with the modems plugged in but no modem drivers
installed. It continued after I installed the modem drivers. (If it helps
any, Windows always identified and installed the modem at COM2 first.)

The Multitech modems were selected in great part because Multitech
guaranteed that they would run together on a Windows box without driver
conflicts. And until the original Pentium III box died, they ran withgout a

But like I mentioned, the problem with the TD/RD display happens even before
Windows has identified and installed the voice modem drivers. When those
LEDs light, the modems are simply two serial devices plugged into COM ports.

What is it about Windows XP on Intel 810-based PCs that causes COM2 to act
so screwy? How do I fix this? I'm out of PCs!


Misbehaving modems are driving me nuts