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Grex Micros Item 182: IRQ Quandry, Win'95 and COM ports....
Entered by zqylli on Sat Feb 14 08:02:35 UTC 1998:

I have a machine with *many* peripherals.
A scanner, a printer, (the usual: keyboard, monitor and mouse), a Zip Drive,
a CD ROM, floppy drive, Aethernet Connection, SCSI card (for scanner), IDE
Controlers, PCI card, and a modem.  The problem: IRQs!  There are only 16
IRQs on my motherboard!  I have many overlaps between those, as the system
seems to think that having 3 COM ports is useful.  Is it?  Is there any way
to get rid of the other two I do not use, so I can free up the IRQ's for other
things?  (Oh, yeah, a sound card is there too..I suppose i could get rid of
that...)  This is a Windows '95 system.  
The current overlaps:

IRQ 14:  Standard PCI IDE Controler/Primary IDE controler (problem??)
IRQ 09:  Standard PCI Card/ PCI Ethernet controler  (there are big question
marks on each of these as well)
IRQ 03: COM4, COM2  (which doesn't seem to be a problem, since COM2 is not
being used)
Looking at these lists, it occurs to me that it could be that the computer
is confused and thinks that there *should* be two devices doing these things
but in fact there are only one..but I don't know.  
Another thing I have thought of is putting all the COM interupts on one
channel...it could be a good idea, maybe not. (then put the Ethernet card
on that leftover, then everything (*should*) be happy.)
If putting all COM interupts on one channel is a good idea, someone gifted
in such areas please tell me how to do it...I'm good but not *that* good. :)
If there is any more info that you need, please let me know here.

2 responses total.

#1 of 2 by zqylli on Sat Feb 14 09:40:30 1998:

Um...scratch that option of putting all the COM ports on one channel.
Can you say, Catistrophic Falure?  I know I did.
Ok, yeah, that makes sense...as COM 1 is the serial port. <duhhhh>
And Win '95, for all it's faults, did manage to save the day (ultimately) by
automaticly re-configuring the COM port during the re-boot process after
the Catistrophic Falure. (boom, crash)  I stand myself corrected.

#2 of 2 by mwg on Tue Feb 24 04:21:21 1998:

If you configure Win95 to use DOS printing calls (write to a file called LPT1
or LPT2) you can steal IRQs 7 and 5 for another device, early sound cards did
this a lot.  If you are not using some Com ports, you might be able to disable
them in your system BIOS, note that on some boards, this actually makes the
hardware inoperable, which clears some problems, but on others, it simply
removes BIOS support and PnP systems like W95 find the hardware anyway and
WILL NOT allow you to not support them.  You should be aware that some PCI
systems support extra interrupts that ISA cards cannot see, you have to look
very carefully at the BIOS settings to find this and see if any of your PCI
cards can respond to it.  To date I have seen systems that use interrupts A
and B on PCI bus slots, there may be more options that I don't know about.

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