Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!rice!uw-beaver!milton!roger
From: roger@wrq.com (Roger Fulton)
Newsgroups: comp.os.msdos.programmer
Subject: Re: problems with com3 & com4
Keywords: com3 com4
Message-ID: <15344@milton.u.washington.edu>
Date: 28 Jan 91 22:18:07 GMT
References: <1991Jan25.054228.157@frey.newcsatle.edu.au> <1991Jan27.034726.15865@meadow.uucp> <22167@netcom.UUCP>
Sender: news@milton.u.washington.edu
Organization: Walker Richer & Quinn, Inc., Seattle, WA
Lines: 15

In article <22167@netcom.UUCP> resnicks@netcom.UUCP (Steve Resnick) writes:
>COM3 & COM4 have defined, standard addresses and IRQ settings. 
>	COM3 Uses a base address for the UART at 3E8 and IRQ 4
>	COM4 Uses a base address for the UART at 2E8 and IRQ 3

COM3 and COM4 do NOT have "standard" IRQ settings.  It is *somewhat*
common for software to default COM3 to IRQ4 and COM4 to IRQ3, but
it is NOT a standard.

The only COM ports whose IRQ's are cast in stone are COM1 (IRQ4) and
COM2 (IRQ3).


Roger Fulton
roger@wrq.com