52702 6AUG89-1621 Hardware Hacking
256K x 4 bit chips
From: LMCCLURE To: MARTYGOODMAN
I recall you once explaining that the reason 256K x 4 bit chips could not be
used on the CoCo is because the CoCo does not support the refresh cycle needed
by these 1 megabit chips. (Wasn’t it 512-cycle vs. the normal 256-cycle)?
If this is what I think it is, there may be a way around it. If my memory is
not to rusty, there may be a way around this. When 256K upgrades first started
coming out for the Atari XL series, it was noted some of the earlier ANTIC
chips did not support the proper refresh. (In fact, I believe they mentioned
it only support 128-cycle, and 256-cycle was needed). As a result, some mods
included a circuit to provide the refresh extension.
I would expect this would work for the CoCo as well, if I have my info straight.
And with 256Kx4 chips going for as low as $15, and 256Kx1 chips going for
about $6 each, some savings could be realized even if the extra chips needed
(I believe the Atari circuit took 3) ate up the savings in power and board
BTW, I don’t plan on doing anything about this if this is possible, as I
already have a 512K upgrade. But I thought some prospective board maker out
there might be interested in if my thoughts are correct…which would mean a
256Kx4 bit chip 512K upgrade would be economically feasible.