Path: utzoo!attcan!uunet!uport!plocher
From: plocher@uport.UUCP (John Plocher)
Newsgroups: comp.unix.microport
Subject: Re: using an above board's serial port
Keywords: above board 286/ps
Message-ID: <456@uport.UUCP>
Date: 5 Sep 88 19:28:43 GMT
References: <297@hawkmoon.MN.ORG> <451@uport.UUCP> <196@dcs.UUCP>
Reply-To: plocher@uport.UUCP (John Plocher)
Organization: Microport Systems, Scotts Valley, CA
Lines: 19

+---- In article <451@uport.UUCP> John Plocher writes:
|In general, IRQ lines *can not* be shared across boards.
+----

+---- In article <196@dcs.UUCP> Wolf N. Paul writes:
|Can one configure the vanilla V/AT 2.3 (or later) driver to use four serial
|Board 1:       First port is  COM1, IRQ 4, Address 0x3f8
|               Second port is COM2, IRQ 3, Address 0x2f8
|Board 2:       First port is  COM3, IRQ 4, Address 0x3e8
|               Second port is COM4, IRQ 3, Address 0x2e8
+----

The problem with "sharing" IRQ lines across boards is the fact that
the hardware which drives the IRQ lines is not open collector logic,
but uses pull up resistors and normal line drivers.  This means that 
if 2 boards (like the comm boards above) try to share the same IRQ lines
there will be hardware problems unless you physically modify the boards.

    -John Plocher