Hi.
************************************
Javier Vizcaino. Ability Electronics. [log in to unmask]
http://www.automodelismo.com http://ability53.hypermart.net
  Starting point:        (-1)^(-1) = -1
  Applying logarithms: (-1)*ln(-1) = ln(-1)
  Since ln(-1) <> 0, dividing:  -1 = 1     (ln(-1) is
complex, but exists)

>     One issue that we cannot find in our host of saved
posts is how one might
>go about installing an additional COM port and an internal
modem in the
>circumstance where one has an external modem utilizing the
same serial port,
>but a different COM port.  In our case, we have an external
modem installed on
>COM4 utilizing IRQ 3, a serial mouse utilizing COM 1 on IRQ
4 and we wish to
>install an internal modem on COM 2 at IRQ 5.

"utilizing the same serial port, but a different COM port"
is not very understandable.
If you mean assign different COM addresses to a physical
serial port (on mobo or i/o card), this is normally
possible, by bios or jumpers.

If you have a mobo with internal COM's you want enabled, and
you firmly want to do as above, you would have to inform the
bios that your other internal COM should have COM3 address
(3E8+). This would surely use IRQ4 (as mouse), so no way if
so.
More normal would be:
-COM1/IRQ4: internal, mouse.
-COM2/IRQ3: internal (16550), your external modem.
-COM3/IRQ5: your internal modem.
You have COM4 address still free. If you want it for still
another modem (!!):
-if internal, the only problem would be finding a free irq;
-if external, you would need a COM4, may be in an i/o card.
If not a 16550 type, it would not be optimum, so you better
move the mouse to this com, changing it to COM1/IRQ4, and
assigning a mobo com to COM4. But then, for using mobo's
coms with external modems, you would need a mobo with the
possibility of assigning other than IRQ4 or IRQ3 to its
com's (avoid mouse irq), which is a rare mobo. If this were
the case, you could use:
-COM1/IRQ4: i/o card com (not 16550), mouse. Why assign a
16550 to a mouse?
-COM2/IRQ3: internal (16550), external modem.
-COM3/IRQ5: your internal modem.
-COM4/IRQx: internal (16550), external modem, and x<>3, 4,
5.
You can, instead, use a PS/2 mouse (IRQ12), and:
-COM1/IRQ4: internal (16550), your external modem.
-COM2/IRQ3: internal (16550), your external modem.
-COM3/IRQ5: your internal modem.
Again , COM4 is free for a serial device or for still
another modem (!!!).
BTW, I'm now at a PC with an Asus TX97 mobo, with four
com's, and a PS/2 mouse. Due to varied reasons, I've
assigned
-COM1 (3F8+)/IRQ9: i/o card, not 16550.
-COM2 (2F8+)/IRQ5: i/o card, not 16550.
-COM3 (3E8+)/IRQ4: mobo (16550), to external modem.
-COM4 (2E8+)/IRQ10: mobo (16550), available.
And if you still want more modems (!!!!), you can look for
multicom cards, common in the Unix world (many com's sharing
an irq, with a driver). If spread com's and more than 4, may
be W95/98 or NT supports them (irq issue?), but DOS (and
many com apps) is limited to COM1-4, since it relies on bios
reserved 8 ram bytes for informing com's on 40:0-7.
You see how many combinations are possible. And if software
(os and apps) writers would not be so lazy, mobo makers
would inform about their internals, and all peripherals
capable of interrupting could identify themselves as sources
of interrupt, irq's could be shared freely except at the ISA
bus (which, BTW, is due to IBM's short mind, doing an
inadequate hardware design on the first PC, inherited for
compatibility on all ISA buses of every single PC built).

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