Date: Fri, 19 Jul 1996 21:30:09 -0700 From: "Michael L. VanLoon -- HeadCandy.com" <michaelv@HeadCandy.com> To: gtc@aloft.att.com (gary.corcoran) Cc: Brett_Glass@ccgate.infoworld.com, alex@fa.tdktca.com, bde@zeta.org.au, E00114@vnet.atea.be, freebsd-hardware@freebsd.org Subject: Re: Multiple COM ports with same IRQ Message-ID: <199607200430.VAA20291@MindBender.HeadCandy.com> In-Reply-To: Your message of Fri, 19 Jul 96 17:35:10 -0400. <9607192135.AA15984@stargazer>
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>One question though: The "open-collector" scheme described above (which is
>what is commonly used for interrupt sharing) works quite well for
>ACTIVE LOW interrupt signalling. But the IRQ lines on EISA (and ISA)
>are ACTIVE HIGH signals. Do EISA PICs also allow the active state of
>the bus IRQs to be changed from high to low? (I don't think so).
>From the vague references I found quickly scanning through my BusLogic
Technical Reference Manual, it indeed appears the state of the signal
is inverted depending on which mode it is running in.
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Michael L. VanLoon michaelv@HeadCandy.com
--< Free your mind and your machine -- NetBSD free un*x >--
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