Not quite... The end of the ROM based PLA for the 64

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eslapion
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Re: The end of the ROM based PLA for the 64

Post by eslapion »

Good news! I have found a new circuit which is not discontinued and will work reliably as a PLA in a C64.

More to come.

Behold PLAnkton!
Last edited by eslapion on Sat Oct 03, 2015 2:59 am, edited 1 time in total.
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Re: The end of the ROM based PLA for the 64

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Ray Carlsen has informed me that he will be testing PLAtypus.
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Re: The end of the ROM based PLA for the 64

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PLAtypus is a success. However, since the advent of PLAnkton, I have decided to leave to others the production and development of (E)PROM based PLAs.

Ray Carlsen is now responsible for the production of PLAtypus.

Also, since there are asian component distributors who sell counterfeit M27C512-90B6, me and Ray have created a very simple device to check for problematic PROM based PLAs. You can connect this device on pins from the PLA socket or at the cartridge port.

Here's a schematic:
Image
You can replace the 74LS279 with a 74HCT279 - DO NOT USE A 74HC279, it will cause false positives

Usage:
1. Make sure no cartridge is connected to the C64
2. At power up, the LED will light up when the C64 checks for the presence of an autostart cartridge
3. Press the pushbutton to turn off the LED and watch for it
4. A good PLA will not reactivate the LED, a faulty PLA will turn the LED back on even if you press the pushbutton multiple times.
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Re: The end of the ROM based PLA for the 64

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After discovering the compatibility problems of Atmel PROMs, it may not yet be the end of the PROM based PLAs.

I still have a good stock of 30 units of PLAkate in stock. But that's not all... I discovered a few things with the logic analyser lent to me by my friend Sylvain.

1st. I was finally able to screen capture what I saw in the ETS lab back in 2008: ST's M27C512-90B6 DOES NOT generate any bus contention at all when used as a PLA on the C64 (neither did many 120ns PROMs and EPROMs tested back then).

2nd. I was able to document the response speed on a number of different PLAs made/sold by Commodore and compare these with various substitutes including the SuperPLA V3, PLAnkton and PLAkate/PLAkate RC (soon to test:MegaPLA from Jim Brain).

3rd. I noted using a special 0.2v diode (1N5819) to reduce the operating voltage of PLAkate increased its level of compatibility with a few special types of carts

4th. I was able to understand EXACTLY why ST's PROM is perfectly OK as a PLA substitute but not Atmel's or Winbond's - Its a matter of slew rate on signaling

Now, I have only 30 PROMs left in stock and although they do have lower compatibility with older boards when compared to PLAnkton, they also have one glaring advantage over it: they consume less than half the power!

PLAnkton is, IMHO the ultimate PLA substitute with 100% compatibility so far with the 82S100 and it consumes about 1/5th the power of the 82S100 at about 22mA current load - almost the same as an LED. PLAkate is less compatible with early boards 326298 and 250407 because its CASRAM latency is too short but it consumes only 10mA, maybe even less according to Skoe.

Also, I noted the M27C256B-90B6 from ST too also has the special "lazy output" that characterizes the M27C512-90B6 - it too has a low slew rate that prevents any and all bus contention from ever being manifested on a C64's bus when used a a PLA substitute. Then the question is: How do you put 65536 possible combinations in a chip that has only 32768 possible entries? Answer: By using two chips and using what was the 16th input as a means of selecting the right chip.

A pair of stacked M27C256B-90B6 can become a single PLA sub and I call this ugly looking but perfectly working contraption sPLAtt.

When tested with a logic analyser, sPLAtt generates EXACTLY the same type of signal as PLAkate but being built around 2 PROMs, it doesn't have the energy saving benefit of PLAkate. I do have 50 of them in stock, giving the potential to make another 25 PROM based PLAs that operate to perfection.

Since I need a logic inverter to select which PROM signals, i used the left over gates from the inverter to increase the CASRAM latency thereby giving sPLAtt the same level of compatibility with older boards as PLAnkton.
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Re: Not quite... The end of the ROM based PLA for the 64

Post by e5frog »

Is there an upside to sPLAtt? Cheaper, less current? Any reason at all to use that instead of a U17 PLAnkton?

Maybe use four 128kb chips - or eight 64kb chips going down to 8kb and create the largest PLA replacement ever seen... ;-)
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Re: Not quite... The end of the ROM based PLA for the 64

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e5frog wrote:Is there an upside to sPLAtt? Cheaper, less current? Any reason at all to use that instead of a U17 PLAnkton?
Well, right now, the only significant advantage is sPLAtt is available while PLAnkton is not. Another potential advantage is the price tag since PLAnkton was 12.67$US and sPLAtt's official price tag is 8.50$US.
Maybe use four 128kb chips - or eight 64kb chips going down to 8kb and create the largest PLA replacement ever seen... ;-)
That would be amusing but apart from generating an ugly looking yet perfectly working PLA replacement, the point of creating sPLAtt is to salvage unused 27C256 series chips which happend to have the same output characteristics as ST's M27C512-90B6; no bus contention or stutters on the outputs.

I don't know of any 27C128 or 27C64 that happend to have the desired characteristics. Otherwise, it would be an incredibly fun thing to do. 8)
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Re: Not quite... The end of the ROM based PLA for the 64

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Let's make it the next big project...


... no I'm kidding. ;-)
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Re: Not quite... The end of the ROM based PLA for the 64

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Just tested my first sPLAtt, works beautifully.

Tested it with the 500MHz logic analyzer, not a trace of bus contention or stutter. Gives a CASRAM latency of 40ns, just about the same as a 82S100, 2ns faster than PLAnkton.

Works well with Fastload, Super Zaxxon & Ms. Pacman
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Re: Not quite... The end of the ROM based PLA for the 64

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I have sold my remaining stock of M27C512-90B6 to Ray Carlsen.

Despite all the claims by Jens Schönfeld and Groepaz, in 8 years using this chip we weren't able to find a single compatibility problem other than the fact it requires an RC filter on CASRAM. This filter is already present on boards 250425, 250466 and the SX-64.

I still use one of these chips on my own 250466 and it works as well as a genuine Commodore made PLA but consumes 90mA less power.
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Re: Not quite... The end of the ROM based PLA for the 64

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For those who want the ugliest looking PLA replacement that's guaranteed to work as well as a genuine Commodore made PLA, sPLAtt is still available for 7.60 Euros or 8.50$US apiece.

Since sPlatt requires a logic inverter to select which one of the 2 PROMs is active, I used a 74HCT14 which has a few extra gates and used 2 of them to introduce adequate CASRAM latency. The consequence is this contraption works well on all C64 boards including the old 326298, KU-14194 and... the C64r.

Reminder: sPLAtt is based on ST's M27C256B-90B6 which has the same output characteristics as ST's M27C512-90B6 thereby eliminating any and all glitches or possible bus contention you would have with the Atmel AT27C512-45PU.

It is covered by the same guarantee as PLAnkton; 90 money back and 3 years afterwards.
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Re: Not quite... The end of the ROM based PLA for the 64

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sPLAtt gave me an idea of another interesting use for a 74HCT14...
Top oshpark preview.png
This nice little board, the SuperPLA FastLoad fixer - sPLAff - created by myself and e5frog will fix the problems with the SuperPLA caused by the fact the Mach210 has no hysteresis on inputs.

It will make the SuperPLA compatible with FastLoad and resolve compatibility issues with older C64 boards 326298 and KU-14194 by adding a few ns of delay to the CASRAM line.

Since the SuperPLA consumes about 60mA of power, about triple the power used by PLAnkton, no improvement is possible there.
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Re: Not quite... The end of the ROM based PLA for the 64

Post by banman »

Hello,

I found this forum a little while ago and wanted to see if I could get a PLA epom based solution to work...


The result is YES!

I got boards made up from this site:

https://oshpark.com/shared_projects/mdayhhyk

you can download the gerbers and take them to any PCB manufacturer you prefer. I also used PCBWay and found their boards better quality and cheaper.

I got M27C512-90B6 EEPROMs from here:

https://www.aliexpress.com/item/Free-sh ... 4c4dLmARaP

I got 5 for about $22 AUD, NOS I think...

Maybe there are equivalents out there, not sure. Please let me know. :-)

I didn't put the delay timing capacitor in (still waiting on the delivery).


Burned a PLA.BIN with a TL866 minipro from here:

http://vic20.de/html/eprom_pla_8296_und_c64.html


It all appears to be working fine so far. I had originally used a Winbond 27C512 45ns eeprom. These worked with lots of screen artifacts on quite a few programs/games.

I have used Moon Patrol & Pac Man cartridge no worries.

Also I have used an original Epyx FastLoad and an original Commodore Magic Desk cartridge without issue.

Mainboard current Draw is between .69 - .70A. The Board a 250425. Everything not too hot.


I am still testing. Unfortunately I don't have an extensive library of Carts/software to stretch the legs on this PLA Eeprom.




Thank you to eslapion , I appreciate the input you put in. :-)
Last edited by banman on Fri May 17, 2019 9:26 pm, edited 1 time in total.
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Re: Not quite... The end of the ROM based PLA for the 64

Post by eslapion »

banman wrote:I got M27C512-90B6 EEPROMs from here:

https://www.aliexpress.com/item/Free-sh ... 4c4dLmARaP
They are fake and they generate tons of glitches but you can only see it when you hook up an oscilloscope or a logic analyzer to them.

You'll start getting bugs when you use sensitive cartridges. The best candidate is Super Zaxxon (the cartridge, NOT the disk version).

Moon Patrol and Pac Man are meaningless catridges to test because they only contain ROM, no logic chips in there.
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Re: Not quite... The end of the ROM based PLA for the 64

Post by banman »

Hi eslapion,


WOW! I didn't know that.


Thanks for the heads up. They look very convincing. I will try to upload an image.

I will look around and see if I can get a cartridge version of Super Zaxxon.


I don't own an oscilloscope. Unfortunately I'm not very technically proficient.


Do you have any other tips for say, a lay person on testing with the eprom based PLA?


I appreciate your feedback on this.
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Re: Not quite... The end of the ROM based PLA for the 64

Post by banman »

Here is a few pictures of some of the chips I received.

It was a grab bag of different types.

These ones physically looked likely candidates.

Sounds like from what you say the sellers are very sophisticated in their counterfeit measures.

Do you have shots of what a genuine label may contain?

I appreciate your time in reading my comments.


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