uVax II questions

From: Eric Smith <eric_at_brouhaha.com>
Date: Fri Feb 26 22:02:49 1999

I wrote:
>> Speaking of such things, can anyone explain how the memory cards in a
>> MicroVAX II or III know where to map themselves? They don't have DIP

Megan replied:
> Basically, the address is passed to the first board. If the address is
> in the range it can handle, it responds and that's it. If not, it
> subtracts its size from the address and passes it on to the next board.
> If the modified address is within the range of memory you have installed,
> eventually one of the boards will see the address as an address between
> zero and it's size, and respond. If no board responds (and the address
> falls off the end, so to speak), then the processor times out and you
> get a non-existent memory response/trap.

This would make sense to me if the wiring was such that there were separate
address busses from the CPU to the first memory card, the first memory
card to the second memory card, etc.

But as far as I can tell, all of the signals are simply bussed in parallel
to all of the memory cards. That's what I find baffling.

Obviously there is a very simple explanation which I am overlooking.
Received on Fri Feb 26 1999 - 22:02:49 GMT