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.