eproms

[Mika Helander]

There is "incompatible" upgrade path from 2716->2764 type of EPROMs but from 
128-512 there is only one added address line per next step to bigger chip. 
That means that if those smaller EPROM n.c. pins are not pulled away from 
socket and connected to ground this "copying" is needed to give data to CPU 
when it reads it.
The real problem in point of CPU view is that if those n.c. pins are really 
not connected in PCB those pins can oscillate - this is chip manufacturer 
dependent.

As a conclusion I suggest that (because nowadays bigger chips are cheaper 
than "old" smaller ones) use bigger one, put EPROM to two stacked sockets 
and glue dip switch in position of the socket it fits, connect other side of 
it to ground pin in socket and other end pins to bigger chip address pins 
(means cut these pins from upper socket and solder wires to those cutted 
pins) which are n.c. in smaller one. Then put that constructed 
EPROM-cutted_socket-non_cutted_socket stack to chip socket in ECU.

I did this kind of "stacking" some 15 years ago when I made my own EPROM 
burner and used those bigger chips in older computers equipped with sockets 
for smalled EPROMs.

-Mika

______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com