USRobotics V.34 - Manual (Page 31)

COURIER HIGH SPEED MODEMS
3-4 Internal Modem Set Up
Select an Interrupt Request (IRQ)
IBM-compatible computers reserve IRQ4 for COM1 and IRQ3
for COM2, as shown below. Some communication programs
support reserved IRQs for two serial ports.
Serial Serial Port
Port IRQ Address (Hex)
COM1 IRQ4 3F8 − 3FF
COM2 IRQ3 2F8 − 2FF
COM3 IRQ4* 3E8 − 3EF
COM4 IRQ3* 2E8 − 2EF
*Select IRQ4 (COM3) or IRQ3 (COM4)
only after reading the following
guidelines:
If you need to use COM3 or COM4, keep the following in mind:
• The Courier supports three additional IRQs: IRQ2,
IRQ5 and IRQ7. Your software must support the one
you use for COM3 or COM4. However, if your
computer is XT-compatible, IRQ5 is reserved for the
hard disk, and it is not available for a serial port. IRQ5
is available on 286-PCs and higher.
• Two devices should not use the same IRQ at the same
time, because there will be a conflict and you will prob-
ably lose data. For example, if you use IRQ4 for a
mouse installed at COM1
and for your modem installed
at COM3 (as shown in the previous table) you cannot
use the mouse and the modem at the same time.
Additionally, if an installed device doesn't use IRQs,
you can use the IRQ normally associated with that
COM port. For example, if you have a serial printer at
COM1 and you know it does not use an IRQ, you can
use IRQ4 at COM3. Similarly, you could use IRQ3 at
COM4 if the device at COM2 doesn't use IRQ3.
If you cannot find the information you need in your software
documentation, call your software's Technical Support Depart-
ment for help in selecting an IRQ. You may find it necessary to
re-install your serial devices to correctly allocate the available
serial ports and IRQs.