Re: 8088 card and bank 15

Den Fri, 27 Oct 2017 05:34:22 +0000 skrev "Baltissen, GJPAA (Ruud)"
<ruud.baltissen@apg.nl>:
> Hallo Michał,
> 
> 
> > Of course it will not work. Even though BP0-BP3 have the correct
> > value, memory access is still governed by RAS and CAS on the J2
> > port which go to DRAM. The chips in bank 15 cannot see these
> > signals.
> 
> Yes, but worse: the 8088 card doesn't provide the needed address
> lines. Completely overlooked that :(

Yes, you'd have to demux the muxed adress lines that's meant for the
DRAM's.

B.t.w. while looking at the circuit diagram my impression is that it
would be rather easy to expand the memory on a CBM-II machine. It could
be done with more banks and/or with larger banks. If opting for more
banks the PLA 82S100 in U75 would have to be complemented with another
with similar content but which treats BP0-3 differently to map the
extra memory in other banks than 1-4. If opting for the same number of
banks but larger memories in one or more banks it's just a matter of
mainpulating BP0-3 on it's way to this PLA. Also if opting for larger
memories there would be a need to substract 1 from the BP0-BP3 signals
and then mux the resulting BP0 and BP1 (or maybe even more signals)
onto "new" inputs on larger DRAMs. Seems rather straight forward.
Either way it would probably not need much special attention to make it
compatible with the 8088 board.

Is the U75 PLA socketed on CBM-II boards? As I understood from this
thread, the first two banks of DRAM is usually soldered directly to the
board while the last two banks is usually socketed. Is this correct?

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