Here's our Windows XP Tip for.. February 6, 2006
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More on Interrupts
In the last tip, we listed some of the common interrupt assignments. This time, let's look at some of the common conflicts.

In general, you can't assign two devices to the same interrupt. That said, we have to recognize that any computer with more than two COM ports is using the same interrupt for more than one device. The trick with the COM ports is that you don't use the conflicting ones at the same time. For example, if you have a modem assigned to COM3 and you attempt to use COM1 while the modem is active, you'll get a conflict. In most cases, this won't cause any drastic problems--COM1 will most likely simply decline to open.

You can also have some problems with sound cards that use interrupt 5 and have a second printer port (LPT2). Once again, you can usually handle this. The only problem is when you use the sound card and LPT2 at the same time.

When you work with interrupt conflicts keep in mind that if two devices must often run simultaneously, you need to assign them to different interrupts. If they never operate simultaneously, then you have no problem with them using a common interrupt.