Networking Technologies and Information

Computer Locks Up After Installing or Using

Internal Modem, Terminal Adapter, or Network

Card.

COM3 shares IRQ4 with COM1, and COM4 shares IRQ3 with COM2 by default. The problem is that

IRQ sharing for ISA devices (such as your COM ports) works when only one device at a time is using

the IRQ. The most likely cause for your problem is that your mouse is connected to COM1, your

internal modem is using COM3, and both COM ports are using the default IRQ of 4. There is no

problem as long as the mouse has IRQ4 all to itself, but the moment you try to use the modem, the

computer can’t handle two devices trying to use IRQ4 and locks up. The only solution is to get the

internal modem and mouse working on

the mouse to another port, or disable COM2 in your computer to make room for an internal modem

on COM2.

ISA network cards and internal ISDN terminal adapters also can cause conflicts with either serial ports

or other devices using IRQs.

You can minimize or eliminate IRQ conflicts by using PCI modems, network cards, and terminal

adapters or by using external USB versions when available. With Windows 95 OSR 2.x, Windows 98,

Windows Me, Windows 2000, and Windows XP, IRQ steering features supported by most newer

Pentium-class chipsets allow multiple PCI-based devices to use the same IRQ without any problems.

If you’re still using a serial mouse, you should consider switching to a PS/2 mouse (which uses IRQ12)

or a USB mouse to avoid serial port conflicts with analog modems. If your system has no PS/2 mouse

port or USB port, consider using the mouse on COM2 instead of COM1 and installing an analog

modem as COM1.

If your system uses Windows 98/Me/2000/XP but doesn’t have a USB port, you can add a PCI card

with USB ports for less than $30, enabling you to connect a USB mouse or other USB peripherals.

COM2, the second serial port, is found on the motherboard of some Pentium-class PCs. If you are

using an ISA modem, you should disable COM2 on the motherboard to allow the modem to use

COM2.

To disable it, go into your computer’s BIOS Setup program, look for the screen that controls built-in

ports (such as Onboard Peripherals), and disable the port. Save the changes and exit the setup program;

the system reboots. To see whether COM2 is disabled, use the Windows 9x/Me/2000/XP System

Properties sheet Device Manager. Then set your modem for COM2, IRQ3 and install it.separate, non-conflicting IRQs. You have two options: Move