13 Oct
2010
13 Oct
'10
11:22 a.m.
On the 2564 the chip is selected when CS1 and CS2 are
both low=2C I thought=
And PD has to be low too. Thatgives you effectively 3 enalbes, and
they're all used for different signals in the MW4 :-(. A13, A15 and A14
ORed with Rd/ So the top 3 address lines and the Rd/ signal all have to
be low to enable the ROM.
perhaps a pair of diodes could be used to feed an OR
of these signals to t=
he OE (active low) on an 2764? If not then a 74LSxxx would have to pressed =
into use.
I think 4000 series CMOS would be better in the MW4. It's what's used
anyway for address decoding, etc. I don't think there are any spare gates
in the MW4, so you would have to add another chip ;-(.
It might be easier to convince one of my programmers ot burn a 2564. If
the original chip is OK part from bit-rot, it should be possible to
program it again.
-tony