Modems - Standard modem settings

Resolving The Problem

You should plan to have your modem use one of the standard settings listed below for the best software compatability even though your modem may support IRQ 2, 3, 4, 5 or 7. It important to make sure that no other device is configured to use the same IRQ and I/O address as your modem.

SERIAL 1	COM1	I/O 3F8h	IRQ 4
SERIAL 2	COM2	I/O 2F8h	IRQ 3
SERIAL 3	COM3	I/O 3E8h	IRQ 4
SERIAL 4	COM4	I/O 2E8h	IRQ 3*

*Avoid COM4 if possible as many video graphics systems share COM4's memory address. Click here for an example. Note the following regarding the above table:

COM1 and COM4 share IRQ 4
COM2 and COM4 share IRQ 3.
IRQ "sharing" often leads to difficulty and is not recommended.

It is not recommended to configure, for example, a serial printer using COM1 and a modem using COM4. Each of these devices would expect to have IRQ 4 for it's own use. You would in this case, get an error message if you tried to use your modem when at the same instant your system (possibly without warning) attempts to access the printer to clear a print job.

Other common sources of conflict include a sound cards and network cards.
You may have to "shuffle" the IRQ of an adapter card to make room for your new modem.

The default IRQ/Assignment table below illustrates which resources may be available should you need to change an adapter's IRQ resource. Your machine may have, for example, a Local Area Network card assigned to IRQ 5.

IRQ	Assignment
0	System Timer
1	Keyboard
2	Cascade Input
3	COM2
4	COM1
5	Available or Parallel Port 2 (LPT2)
6	Diskette Controller (floppy drives)
7	Parallel Port 1 (LPT1)
8	Real-time Clock
9	Available
10	Available
11	Available
12	Mouse
13	Math Coprocessor
14	IDE Drive 0,1 (If installed)
15	Available

Keywords:
COMM, Modem, Standard Settings