My condolences on your defunct PLAnkton module.Borat wrote:So what is the best solution to the PLA replacement issue at present? Is it the M27C512-90B6 or PLAnkton (and the likes)?
The answer to your question depends on the type of mainboard you have, your budget and your technical know how.
PLAnkton is the easiest and most compatible replacement solution that works on all C64 boards except the C64c's assy 250469. PLAnkton is the only solution I recommend for older boards like the 326298, KU-14194 and 250407.
However, if you know you have a board with a built-in CASRAM RC filter - these include boards 250425, 250466 and the SX-64, you have a fairly good amount of technical know how and want to save money (usually because you want to repair many C64 boards) then the (E)PROM based solution may be for you.
If you can lay your hands on a genuine M27C512-90B6 (I have a few left and Ray Carlsen has a few dozens) then all that's needed is to make an adapter as per the plan provide here: http://www.vic20.de/html/eprom_pla_8296_und_c64.html
Jim Brain also sells adapter boards which require only a 28 pin DIP socket and a set of 0.1" spacing pin headers. Last time I checked these boards were 1.50$US each.
If all you can find is the Atmel AT27C512R-45PU (still in production and available from Mouser and Digikey) then you have to make an adapter and add to that the filtering detailed by Ray Carlsen's documents.
If you're an engineer or an experienced technician then power figures may also play a part in your decision. A genuine Commodore PLA usually requires slightly less than 100mA to perform its job. Since the source power is fed at 5Vdc then 5V * 0.1A = 0.5 watts of power and this chip produces that much heat dissipated on this small size and so it becomes hot. That's the main cause for failure.
* PLAnkton requires only 22mA because it uses a CPLD operating at a fraction of its real maximum speed - me and Fredric tuned it for slower speed.
* The power requirements of the M27C512-90B6 was measured at 8mA. It's an older memory chip by today's standards but since it's not really a logic chip, it runs at its fastest speed when used as a PLA and it uses very little power. It can only be used as a logic chip in a C64 because it's such a slow machine by modern standards.
* The AT27C512R-45PU is the latest (and may be the last) parallel PROM chip on the market and it uses a measly 5mA - that's nearly 20 times less than a Commodore IC.
Please note this thread was started because Tynemouth Software suggests a procedure to use the AT27C512R-45PU as a PLA replacement but mentions absolutely nowhere the necessity for signal filtering.
PLAnkton also signals at 0 - 3.6 volts exactly like a genuine Commodore PLA (TTL-LS levels) while PROM based solution signal at 0-5V. Tynemouth is also wrong in saying low voltage ICs require voltage adapters for that reason.