The Dos and Don'ts of using an EPROM as PLA in a C64.

Disk drives, Monitors, SuperCPU etc.
banman
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi eslapion,


I have made some observations with several Commodore PLA substitutes.

I was having some difficulty uploading more than 15 minutes worth of footage. I have it fixed now....




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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi eslapion,


Here is an observation I made on testing the trigger level on a Commodore factory PLA.



Apologies for the video being upside down. I will try to remedy this..
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi eslapion,


Here's the video the right way up..

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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by Zibri »

Question: is the M27C512 the only cheap eprom suitable for this?
I am sure there must be some new ones usable or adaptable (voltage translation) for this purpose.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by eslapion »

Zibri wrote: Sat Aug 29, 2020 5:41 pm Question: is the M27C512 the only cheap eprom suitable for this?
I am sure there must be some new ones usable or adaptable (voltage translation) for this purpose.
Note to Melon: the forum just flushed everything I typed so here I go again...

I suggested to banman a few 64k x8 memory chips available at Mouser and Digikey but he doesn't seem to have investigated. Since these are rather fast, there will likely be a problem with the CASRAM latency. I suppose a filter or a pair of logic buffers would help avoid problem with RAM access.

Because of the easy availability of the XC9536XL, IMHO, it's a slightly more complex solution but it's pretty much the best. PLAnkton EV adds a voltage correction and extra latency on all outputs to make it even closer to a genuine MOS 906114-01.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
banman
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman »

Hi Zibri,


I would say there are undoubtedly other candidates for an E/PROM based PLA substitute.


I believe eslapion sells a PROM PLA replacement called sPLAtt. It uses 2 x ST's M27C256B-90B6 and some associated hardware.

viewtopic.php?t=2445&start=30


Ray Calsen has managed to to get an Atmel EEPROM to correctly work with some added components to adjust the slew rate.

https://www.elektronik-technik.biz/list ... =S-O=A.htm

I have still to test some E/PROMs that are not knockoff ST branded ones (they are still knockoffs).

I do want to get some original branded E/PROMs from Mouser and Digikey to investigate as eslapion has suggested. I haven't had a chance to get on to it.

Regarding the E/PROMs that I have used. The production date codes are a little old. I would think that chips like these are no longer in production. I think the PLAnkton PLA uses new components that are still in production.

I found the use of E/PROMS as a substitute PLA a very fascinating discussion and informative.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by Zibri »

Mine was just curiosity. I have no doubts whatsoever that the Plankton is the best solution available.
It just seems strange that there is no other eprom with the "right" timings and voltages except those.
Oh and please, don't get too "close" to the original!!! They burned like matches :D
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by eslapion »

Zibri wrote: Wed Sep 09, 2020 3:58 am Mine was just curiosity. I have no doubts whatsoever that the Plankton is the best solution available.
PLAnkton EV is even better.
It just seems strange that there is no other eprom with the "right" timings and voltages except those.
Oh and please, don't get too "close" to the original!!! They burned like matches :D
No EPROM solution has the right 'timing, not even the SM27C512-90B6. The latency on the CASRAM output is too fast and using an RC filter is suggested on older boards. Using 2 inverters from a 74HCT14 will also do.

Be assured I don't intend to emulate the boron chemical bug of the original MOS 906114-01.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders
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