> On Dec 25, 2015, at 2:21 AM, Bob Supnik <[email protected]> wrote:
>
> ...
> So either no core is selected or multiple cores are selected. Now what
> happens? I suspect it's something bad.
FWIW: given how core works, if more than one core select line is active, the
read cycle will see the OR of the two selected cores (since either of them
magnetized will produce the pulse due to the magnetization flip). On the
restore (write) cycle, assuming a single global inhibit line it will write the
same to both cores. So you're going to see the OR of the two words, if the
core uses 1 for magnetized cores (AND otherwise).
If you have segmented inhibit, as in the CDC 6000 core modules, things get more
interesting. Suppose the inhibit decode is working right but the X or Y decode
has a fault, and the two cores selected are in different inhibit regions. If
so, the read would produce the OR of the two bits, and the write would restore
the core whose inhibit is driven, but you'd get a 1 in the other core since its
inhibit is not active.
I suppose this sort of thing could happen in the wild with a fault in the
select logic, which explains where there are "no dual address" memory
diagnostics.
paul
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