From: hartung@crl.ucsd.edu (Jeff Hartung)
Newsgroups: comp.sys.ibm.pc.hardware,comp.os.msdos.misc,comp.os.msdos.programmer
Subject: Now I've seen everything!
Keywords: COM port I/O card IRQ conflict peripheral
Date: 10 Sep 92 17:50:17 GMT
Followup-To: comp.os.msdos.misc
Distribution: usa
Organization: University of California, San Diego


Well, here's a weird story.  I had recently upgraded my motherboard to a 33
MHz 486 from a 20 MHz 386SX (what a difference! :-)  That's not the story, but
while I changed the motherboard, I had reset the jumper on the I/O card so
that COM2 was active.  (I had previously disabled it beacuse I needed IRQ 3
free for the ProAudio-16 sound board's SoundBlaster compatibility jumper
setting.)  Anyhow, I had decided that the 486 could probably handle IRQ
sharing better than the earlier CPU, especially since COM2 usually just sits
there unused.

Everything was working fine for several days until about 1/2 an hour ago when
a Telix session I was running under Windows suddenly froze up and wouldn't
even let me hang up.  (The "hanging up" message just hung there and the screen
and wouldn't go away.)  I finally decided to use the "Terminate" option from
Windows to end the program.  When I restarted Telix, it reported that it could
not initialize COM1 and that I needed to choose another port.  I looked at the
modem, realized that it was still on line, and decided that must be the
problem, so I turned the modem off and on and restarted Telix.  Same message.

"OK," I said to myself, "Windows must be screwed up.  I'll restart it."  (I
talk to myself and my computer when things start to go wrong, do you? :-)
That didn't work.  I exited windows, warm booted, and started it again.  That
didn't work.  I cold booted.  That didn't work.  I checked the Port settings
from the control panel.  They were mysteriously set (for COM1 and COM2) to 
port 02F8, IRQ 4.  Although Windows let me change the settings, when I opened
the Port dialig box, the setting for the port would go back to 02F8.

I figured the WIN.INI file must be messed up and looked at it.  Nope, there
was the port and IRQ setting I wanted (03F8 and IRQ 4).  I tried starting
Telix under DOS.   SAME PROBLEM!!!!!  Uh oh, maybe this was a symptom of an
I/O card going bad!  I rebooted the machine again, this time powering it all
the way off.  When it restarted, the BIOS/CMOS settings screen reported only
one COM port at 02F8.  Ouch!

Fearing the worst, I opened the case and looked at the settings on the I/O
card.  The first port was set to COM1, the second to COM2, but when I looked
at the IRQ settings, I saw that BOTH ports were set to IRQ 4!  "Ah ha!" I
shouted, still talking to myself, and now to an I/O card as well.  "That's
what was wrong.

I quickly placed the COM2 jumper on  the IRQ 3 pins where it belonged and
everything returned to normal.  However, I started wondering, if there was a
conflict, why were both COM ports showing up until now on the AMI BIOS startup
screen?  If the ports were happy sharing the IRQ, why did they suddenly stop
being so friendly to one another?  Why wouldn't even a complete power down
restore the system to its original state?  If there had always been a
conflict, why did things _ever_ work in the first place?

I have two working theories:

	1.  A supernatural being crept into my system via the connection
	    to the UNIX host where I was reading my mail and changed my
	    jumper from IRQ 3 to IRQ 4.

	2.  Windows 3.1 has added an undocumented "Make Random Changes to 
	    System Jumpers for No Reason Whatsoever" feature that was
	    activated my my insistence in using a DOS program for my
	    telecommunications needs.

However, I'd be willing to hear from those who have alternate explanations.

Cheers,


-- 
 --Jeff Hartung--  	
 Disclaimer: My opinions only, etc., etc., BLAH! BLAH! BLAH!...
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