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From: cds@atelabs.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: DOS 3.3 supports up to 4 COM ports - for PS/2 (?)
Message-ID: <236@atelabs.UUCP>
Date: Tue, 26-May-87 17:43:41 EDT
Article-I.D.: atelabs.236
Posted: Tue May 26 17:43:41 1987
Date-Received: Fri, 29-May-87 00:56:13 EDT
References: <335@cgcha.UUCP>
Reply-To: cds@atelabs.UUCP (David Shanks)
Organization: AT&E Laboratories, Beaverton, OR
Lines: 23
Keywords: COM1, COM2, COM3, COM4, port, serial.

In article <335@cgcha.UUCP> whna@cgcha.UUCP (Heinz Naef) writes:
>        Device  I/O Addr Range  IRQ   Comments
>
>         COM3     3E8 to 3EF    5 *)  steals IRQ and disallows use of LPT2
				 ^^^^
I'm only posting this because I've seen this mistake in a couple of postings
recently and don't want others to act on mis-information.

IRQ 5 is NOT dedicated to the printer (at least on an XT).  It is dedicated
to the fixed disk.  The IRQ that is dedicated to the printer is IRQ 7.  In
truth, I don't think any "standard" printer adapter drivers actually use
this interrupt under MS-DOS.  This information is taken from the IBM XT
Technical Reference.

BTW, the fixed disk will stop working if you steal its interrupt.  This is
from personal experience.  (When Microsoft first came out with a bus mouse
they suggested you set the bus board jumper to use IRQ 5.  Guess what that
did to hard disk users.)
-- 
Dave Shanks                     ..!tektronix!tessi!atelabs!cds
AT&E Laboratories               cds@atelabs.UUCP
1400 NW Compton  Suite 300      (503) 690-2000
Beaverton, OR  97006