On  5 Jan 99 at 9:47, Lawrence Gurley wrote:

> From my failing (biological, not silicon) memory:
>
> COM1 and COM3 are the same physical device (as are COM2 and COM4).  You
> can't use both at the same time.

  NO.  COM1 and COM3 have different physical device addresses.

  By default, they use the same IRQ line, and the way ISA bus handles
IRQs doesn't allow both to use it at once.

  I have a couple of systems with PDAs connected -- at least some of
the time -- to COM1, and internal modem on COM3.  The crucial
difference is that these PDAs only use the port when I run their host
support software, and as long as I don't try to do that and go
online, I'm fine.  I think the original poster's problem arises
because the CE device and the PC want to chat all the time, and in
that case either that COM port or the modem must move to a different
IRQ.  [Or switch to a PS/2 mouse on IRQ 12 and arrange these devices
on COM1 and COM2....]

David G

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