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From: resnicks@netcom.UUCP (Steve Resnick)
Newsgroups: comp.os.msdos.programmer
Subject: Re: problems with com3 & com4
Keywords: com3 com4
Message-ID: <22214@netcom.UUCP>
Date: 29 Jan 91 17:07:19 GMT
References: <1991Jan27.034726.15865@meadow.uucp> <22167@netcom.UUCP> <15344@milton.u.washington.edu>
Organization: Netcom- The Bay Area's Public Access Unix System {408 241-9760 guest}
Lines: 32

In article <15344@milton.u.washington.edu> roger@wrq.com (Roger Fulton) writes:
>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).

I dunno, every, I mean *every* serial adaptor I have used which had settings
for COM3 and COM4 used the same IRQ's as COM1 and COM2. I suppose you could
take over the IRQ for LPT1 or LPT2 (IRQ7 and IRQ5) but those are the only
available IRQ's on the Master (and on an XT only) PIC. IMHO, the ideal
IRQ's to use would be 3 & 4, although if you used the printer IRQ's you
might get better interrupt service, but I have never tried this ....


Cheers!
Steve

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