Re: PAL card: I think I've got it but...

[mjmahon@aol.com (Michael J. Mahon)]

Linards Ticmanis wrote:

>Actually I meant pins 23 & 28. Those seem to see even less use. Almost 
>all cards connect them straight through.
>
>What's the protocoll for those "chains" anyway? They only connect the 
>cards to each other, not to any other thing on the motherboard. If 
>they're used for arbitration, wouldn't they stop working when even one 
>slot is empty?

Yes, all slots "up to" the last one arbitrating must be filled, perhaps simply
with "pass through" cards.

A card that arbitrates does not pass the signal straight through, but gates
it through if it is not making a request.  In this way, the lowest numbered
card making a request is the only card requesting the signal (say, DMA)
which sees the priority level (DMA IN), and thus wins the arbitration and
the right to assert the corresponding signal on its behalf.

There are, of course, timing considerations, as well.

-michael

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