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Computer IRQ

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by petadove

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I recently came across some IRQ information that baffled me and I wondered if someone can help.

As I have known for sometime there are 16 IRQ's on a system (0-15); however, I just came a accross a Compaq system that has more listed. The SoundMAX Ingegrated Audio IRQ is listed as 17.Can you tell me how they were able to achieve this feat???

Thanks
Petadove

3 replies

by mcs-1

They accomplish this by multiplexing. By reading the IRQ list on one clock burst the computer reads 0-15. The next clock burst the computer reads the shadow IRQs of 16-31. This is the really simplified versio, and obviously there is a bunch more to it .... but seeing IRQ17 can be a normal thing.

by petadove

Thanks MCS-1; I will do some more research. I just wanted to be sure that I am not losing it.

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