seeking Motorola M68MM01A2 documentation
chrise at pobox.com
Tue Jan 18 14:14:35 CST 2022
On Tuesday (01/18/2022 at 02:01PM -0600), Mike Katz wrote:
> I think it might be easier to modify the 680 prom for the I/O addresses of
> the board rather than modify the board to match the ROM.
Agreed-- except the goal, which I failed to elaborate on, is to come
up with an Altair 680 development environment so that someone can port
some code to the platform without having the real thing. I wanted to
make that environment as close to real as possible (without having front
panel switches and LEDs)-- which means having the I/O in the same place
as the original as well as the authentic PROM code running.
> Especially if the address decoding for the I/O is done in PAL (10L8 for
No PALs on the board but there is a bipolar PROM (82S129). I'm not
adverse to making a new one of those or bodging something that drops
into that socket to modify the decoding if neccessary. I was just hoping
to not have to butcher the board itself too much.
> Some 6800 address decoding was done with 74LS138s. This had the potential
> to be inefficient in terms of memory usage or if the '138s were cascaded
> then propagation delay could become an issue.
Yes. This seems to be a limited function CPU board and I suspect it takes
that approach just to get the four PROMs and I/O decoded very coarsely.
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