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From: jamaass@bluemoon.uucp (Jeffrey A. Maass)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: sharing hardware interrupts
Message-ID: <08VP31w164w@bluemoon.uucp>
Date: 29 May 91 16:41:44 GMT
References: <1991May29.014824.16278@ux1.cso.uiuc.edu>
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phil@ux1.cso.uiuc.edu (Phil Howard KA9WGN) writes:

> I have read that two devices cannot share and concurrent use the same
> interrupt (IRQ).  I'd like to know if this is really so true and if it
> is more a case of just dumb software (which abounds in this world).
> 
> Given the above software, why could it not be possible to have two or
> more devices share the same interrupt.
> 

Phil: You _CANNOT_ share interrupts on a PC/XT/AT, and the reason
is in hardware, not dumb software. Having spent a couple of months
trying to do same before being told the reason, I'd hate to see 
anyone else have the same fate!

Having said that, I can't find the magazine article that "set
me straight", and I don't recall the details as to why (has to do 
with the leading-edge-triggered" nature of the interrupt hardware,
I think).

Anyway, don't do it!

Jeff Maass                   Amateur Radio: K8ND (@ W8CQK)
Powell OH (NW of Columbus)         Netmail: jamaass@bluemoon.uucp
                                   Ma Bell: (614) 873-3234