Path: utzoo!attcan!uunet!cs.utexas.edu!rutgers!att!alberta!ubc-cs!van-bc!unifax!sl
From: sl@unifax.UUCP (Stuart Lynne)
Newsgroups: comp.unix.microport
Subject: Re: Using AST 4port or clone on uPort (long)
Keywords: AST 4port ttypatch technical electronics
Message-ID: <124@unifax.UUCP>
Date: 16 May 89 09:15:38 GMT
References: <701@tukki.jyu.fi> <705@tukki.jyu.fi> <104933@sun.Eng.Sun.COM>
Reply-To: sl@unifax.UUCP (Stuart Lynne)
Organization: Wimsey Associates
Lines: 36

In article <104933@sun.Eng.Sun.COM> plocher@sun.UUCP (John Plocher) writes:
>In article <705@tukki.jyu.fi> makela@tukki.jyu.fi (Otto J. Makela) writes:
>>the motherboard COM2 and used IRQ3, all worked ok.  The big question now
>>is, how does one define "different cards" ?

>Normally, each CARD will have ONE of these circuits on it, so the
>directions say "one card per IRQ".  Cards that have several
>ports on them usually have one driver circuit per IRQ line,
>and the on-board electronics takes care of gating the "I want to
>generate an interrupt" signals from the ports together before 
>the driver circuit sees them.  This means that you could have
>an 8 port card with 4 ports using IRQ3; the BUS level IRQ signal
>is generated by only ONE IRQ driver circuit.

Generally this is correct. 

Notwithstanding some manufacturers still get it wrong. For example with the
AST Advantage. It has two serial ports, COM1 and COM2. This can be enabled
as none, one or two. Also with some options on where to send the interrupts.
But you must send them to separate IRQ lines. You can't double them up!!!

So be careful. While you can usually assume that multiple ports on a
single card can be mapped to a single IRQ, you sometimes can be screwed up.

On the other hand if the manufacture takes care he can allow you to have
multiple cards on one IRQ. For example the Bell Tech Hub 6 allows up to four
boards all using one IRQ. Each card has a switch to tell it whether to
ground the signal. Only one should be turned on. 

The only problem with high number of serial ports on a single interrupt is
that it takes significant amounts of time to check all of the ports to
verify that they didn't generate the interrupt.


-- 
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