Subject: Re: SE/30 PDS question
Date: Thu, 24 Nov 2005 09:48:21 -0000
From: "Brierley, Paul" <[EMAIL PROTECTED]>
This seems such a simple idea, I can't believe it never occurred to me
before!
However, the Asante card does have a series of jumpers for setting the
card "id" so that it doesn't conflict with whatever is in the
passthrough slot.
It seems quite feasible that these jumpers would simply affect the
card's timing with respect to the system bus. If that is indeed the
case, then we could just be looking at two cards connected in parallel.
Hmmm... Maybe I should dig out a voltmeter and do some studying...
I'm pretty sure that the jumpers set which chunk of address space the
card uses.
In other words, the driver for the card provides the software support
so that the CPU can send data to certain addresses which are not in
RAM or any of the built-in IO. The PDS card watches for those
addresses on the address bus (through the PDS slot) and when a
transaction comes along destined for a certain set of addresses, the
PDS card handles that transaction.
The available address space is allocated to "slots" which would be
the NuBus slots in a machine with NuBus. So you can change which
"slot" the PDS card is pretending to be in. All it really changes
is which set of address the PDS card uses. But since you don't want
two PDS cards trying to use the same set of addresses, it's good to
be able to change one card's address.
Jeff Walther
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