26 Feb
1999
26 Feb
'99
1:53 p.m.
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
switches or jumpers, and neither the backplane nor the ribbon cable
seem to provide any distinct signals per slot, except maybe bus grant and
I don't see how they would use that.
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.
Megan Gentry
Former RT-11 Developer
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