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1995-02-01
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February 1, 1995
Hayes Tech Tip -- Installing a Hayes Internal Modem
---------------------------------------------------
When you install an internal modem, you must assign it a unique COM port
setting. If your modem is set to use a COM port that is being used by
another device, you may experience COM port or interrupt conflicts.
Symptoms of COM Port and Interrupt Conflicts:
The communication software cannot find the modem.
Your PC locks up when accessing the modem
The modem doesn't respond to AT commands.
The modem works in some applications, but not in others.
The modem used to work, but doesn't anymore.
The serial mouse doesn't function properly.
<S>topD
Standard COM Port Assignments
The COM port that you select for your modem specifies an address and IRQ
setting. The address tells your computer where to find your modem, just
like a street address. The IRQ setting is used by your modem to get your
computers attention. The table below outlines the standard address and
interrupt settings for each COM port.
COM Port Address Interrupt
------------------------------------------------------
COM1 03F8 IRQ4
COM2 02F8 IRQ3
COM3 03E8 IRQ4
COM4 02E8 IRQ3
Resolving Interrupt Conflicts
COM port or interrupt conflicts can be resolved by selecting a unique
COM port setting for the modem. There are several steps you can take to
prevent COM port conflicts.
<S>topD
Identifying Serial Ports Already Being Used In Your Computer
First, it is a good idea to determine how many serial ports are on the
PC without the modem installed. You should refer to the manual or
documentation for your computer to find information regarding serial
port addresses and IRQ assignments. This information will give you an
indication of which addresses and IRQs are already being used by your
system.
Most computers have one serial port configured as COM1 and have COM2
unconfigured. This setup will allow you to select COM2 for the internal
modem since it is not in use by the system. However, if your system has
two serial ports, COM1 and COM2 before you install the modem, you will
not be able to install the modem on any of the standard serial ports.
You will not be able to select COM3 or COM4 because they share the IRQs
with COM1 and COM2.
There are two solutions to this type of problem.
Solution 1: Disabling Serial Ports
<S>topDThe first solution is to refer to your computer documentation for
directions on disabling one of the serial ports. If you disable COM2 in
your systemAs configuration, you will be able to select COM2 for the
internal modem.
Solution 2: Selecting Non-Standard Interrupts
The second solution is to select a non-standard interrupt setting for
the modem such as IRQ2, IRQ5, IRQ9, or IRQ15. You should find
information in your modem documentation on how to select non-standard
IRQs. In situations where nonstandard IRQs are needed, IRQ5 is usually
recommended since most computers do not use IRQ5. However, some devices
such as sound cards, network cards, a second parallel port, CD-ROM
interface cards, tape backup interface cards, SCSI interface cards, and
scanner interface cards can use IRQ5. If one of these cards is
installed in your computer, check the IRQ level of that card before
selecting IRQ5 for the internal modem. If IRQ5 is being used, you can
change the IRQ level of that card and select IRQ5 for the modem.
Configuring Windows Programs
If you are using Windows, advanced settings for serial ports can be
<S>topDfound in the Control Panel. Changes made in Control Panel apply to all
Windows- based communications programs. Once configured in Control
Panel, you may select the COM port in the communication application
without having to change the IRQ level in the program.
Configuring Your Communications Software
After you have determined which COM port will be used for the modem, you
must configure your software to the communications port and IRQ level in
which you have selected for the modem. If you have selected a
nonstandard interrupt for the modem, you must configure your
communications software with the proper settings to find the modem.
Normally there is an advanced installation or port assignment screen
where you can change the address and IRQ level of serial ports (Some
DOS-based programs does not have this feature).
Contacting Hayes Customer Service
If, after reading through this Tech Tip and trying the recommended
solutions, you are still unable to isolate or resolve a problem, contact
Hayes Customer Service at the following numbers:
<S>topD
World Headquarters
Tel. 404/441-1617
Fax 404/449-0087
Hayes Online BBS 404/446-6336
Asia Pacific (Hong Kong)
Tel. 011-852-887-1037
Fax 011-852-887-7548
Hayes Online BBS 011-852-887-7590
Europe
Tel. 011-44-252-775544
Fax 011-44-252-775511
Hayes Online BBS 011-44-252-775599
Hayes is a trademark of Hayes Microcomputer Products, Inc. Other
trademarks mentioned are the property of their respective companies.
Copyright 1995 Hayes Microcomputer Products, Inc. All rights reserved.