-----Original Message-----
From: Sean Breheny <shb7@CORNELL.EDU>
To: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Date: Sunday, October 05, 1997 14:55
Subject: Re: More ISA bus questions [OT]
>>    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
>>
>
>I know that this is not the ideal design, but I'm not sure that my device
>will be the only one touching the IRQ line. But this ought to work
>(sort-of) because it is possible to have two com ports (1 and 3 or 2 and 4)
>on the same IRQ but on different cards, right? I know they won't work well

    Well yes, the problem is they fight with each other if their outputs
aren't tri-stated, for example one card might be hollding a low and another
might be wanting to initiate an IRQ, the high fights with the low and three
things can happen, 1. the high beats the low enough that the line sees a
high and everything works fine, 2. the high and the low are equal in which
case you've got something between a high and a low, then it depends on the
computer on how it will deal with it, 3. the low beats the high and the bus
never sees the IRQ. Usually everything works fine, but I don't know what the
recommendation is, whether to leave it tristated or not, for stafety sake on
any bus, I would recommend tristating when not in use, it just solves many
problems.

>simultaneously, but they should be able to be in the machine at the same
>time. (I hope) Actually, at the present time, I think that I do have one
>free IRQ below IRQ8.

    I just though about this, I also have one free, IRQ 7, not the best IRQ
to use, probably why it is free in almost every machine I use! :)

>I've already started soldering parts onto my board, and it has only an
>8-bit ISA edge card, so that's the way I have to go. I only need to do
>8-bit transfers at a time anyway.

    Well then, you will be stuck with IRQs below 8, not neccessarily a bad
thing, or a good thing for that matter. :) TTYL