-----Original Message-----
From: Sean Breheny <shb7@CORNELL.EDU>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Sunday, October 05, 1997 13:13
Subject: More ISA bus questions


>Hi again guys,
>
>I've got two more ISA bus questions for the ISA card I am working on. #1)
>When I don't want to cause an IRQ, must I tri-state my lines that go to the
>IRQ pins or can I just hold it low? #2) How can I cause an IRQ greater than
>IRQ7?


    Well, my guess would be to hold it low, since you're device is supposed
to be the only one that touches the IRQ line, however for the sake of
designing something that will help in conflict resolution, try leaving it
tri-stated, if it still works fine leave it, if on the other hand you start
getting spurious IRQs then keep it low, there might be noise on the line. As
for an IRQ greater than 7, you have to access the 16 bit portion of the ISA
bus, meaning you actually need a 16 bit connection, if you're card is 8 bit
you won't have access to the higher IRQs. If you do have a 16 bit card, then
I believe the higher IRQ lines operate almost identically to the lower
lines.

>Also, It would be great if someone could point me to a web site with info
>on the ISA bus.

    Ask IBM, they should have something. Although it might take a while for
them to find it.

>BTW The ISA card I am building is a high speed bidirectional 8bit parallel
>interface card, specifically designed to interface with digital circuits
>that I build, such as PIC based circuits.

    If by 8bit connection to the ISA bus, then no, you can't use the higher
IRQs, if OTOH you change you're card to the 16 bit size it should work, if
fact I don't think you even have to do data transfers with 16 bit, I beleive
it will still allow you to do 8 bit transfers if that is what you want. TTYL