Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!brutus.cs.uiuc.edu!apple!vsi1!v7fs1!sv
From: sv@v7fs1.UUCP (Steve Verity)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Interupt conflicts
Message-ID: <487@v7fs1.UUCP>
Date: 23 Aug 89 20:12:31 GMT
Reply-To: sv@v7fs1.UUCP (Steve Verity)
Organization: Video7, Cupertino, CA
Lines: 26

>>is to make all the interrupt line drivers open-collector. This means that
>Not in PCs it isn't.

>>but the drivers ARE usually still open-collector
>No, you're wrong.

[flame deleted]

>For your information, not that you seem to care, interrupts on the PC
>bus are active HIGH. 

	...So, Do you think that an I/O channel board is allowed to
grab the IRQ line, and yank it low, until it needs to generate an
interupt, at which point, it drives the line high???

	Yes, the interupts on the AT are active high. When a board
wants an interrupt serviced, it must first pull the line low *WITH AN
OPEN COLLECTOR DEVICE* and then let it *FLOAT* high. (these lines are
pulled up on the I/O chanel.)

>--
>Phil Ngai, phil@diablo.amd.com		{uunet,decwrl,ucbvax}!amdcad!phil
>"Nonviolence works! India hasn't had to use their nuclear weapons yet."

Steve Verity
...ames!vsi1!v7fs1!sv