IBM 56K Modem, Installation Manual

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56K Modem Internet Kit
6-8
expansion slot to run an external hard drive, or CD-ROM, or perhaps to
connect to your network. Some video cards also use an IRQ. The main issue
to watch for with video cards is that a lot of them share COM4's memory
address space. This can conflict if you try putting a modem on COM4. Please
contact your graphic card company for support on this issue.
You need to determine which COM Port and IRQ each serial interface card in
your system is using. One way to find this out is to open up your computer,
take out the expansion card or cards, and examine their jumper settings (be
sure the computer is turned off before removing an expansion card). Another
simpler way is to use Microsoft's Diagnostics program.
Using Microsoft Diagnostics for Windows 3.1x users:
Microsoft Diagnostics is a program included with most versions of MS-DOS.
This program tells you what is installed on each COM Port and IRQ. Simply
type MSD at the DOS prompt. If you are in Windows 3.1 or Windows for
Workgroups, exit Windows completely, then run MSD. Look under IRQ
Status and COM Ports. If COM3 or COM4 is available, it will be labeled
N/A. We do not recommend COM4, due to the potential graphics card
conflict mentioned above. MSD is not part of Windows 95 or 98.
IRQ Shuffling:
Sometimes it is necessary to change the IRQ setting on an expansion card to
free an IRQ for the modem. For example, if your sound card is using IRQ5,
you can reinstall it using IRQ11. This would then free IRQ5 for use by your
modem.
Determining a COM Port and IRQ to use for your Modem:
The IRQs available for your modem to use depend on your computer setup.
Each IRQ on your computer is assigned a peripheral device or other function
(you can consult your computer documentation to see what these default
settings are, or use MSD, as explained above). The typical assignment for the
first eleven IRQs are listed below:
IRQ Assignment
0 System Timer
1 Keyboard
2 Cascade input (mandatory function)
3 COM2
4 COM1
5 Parallel Port 2 (LPT2)
6 Disk Controller (All internal floppy drives)
7 Parallel Port 1 (LPT1)
8 Real-time clock interrupt