Dave Park wrote:
> I just need to check out the chip select lines on the two ROM sockets to see
> how they operate - someone has said that in the $8000 socket, CS asserts for
> the entire 32K block, but to me that suggests a conflict with the ROM port.
>
> I'll want to check it out, unless someone can definitively explain the
> address decoding logic from $0000 to $C000... Tony?
My proper schematics copy is at my parents and all online versions are
appallingly bad scans... but so far it looks like A14 is routed to a
second CE on the 23128 ("CE2", active high, acting as A14 for the chip
here) and A15 is connected to -CE (Pin 20, active low!) on the 23256
and CE (Pin 20, active high!) on the 23128. ROMOEH is connected to -OE
for both chips, so it seems to decode the whole lower 64k. The ROM
port will have to do its own decoding it seems.
All this trickery finally explains to me why my innocent try to just
put a 27256 and a 27128 as replacement in 10 years ago were bound to
fail...
Cheers, Marcel
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