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

[eslapion]

@banman

It should be mentioned the type of C64 board you have used for your tests is a 250425 which has the CASRAM delay filter built-in. On these boards, the PROM based PLA solution will work ok even if it is too fast compared to a genuine Commodore PLA. The same is true of boards 250466 which differs only by the type of DRAM chips used.

You will get no such reprieve on the old 326298 or early versions of the 250407. On these boards, the correct response speed is mandatory.

[banman]

Hi eslapion,

OK, very interesting.

I actually did briefly read about this somewhere else, however there wasn't a clear explanation on the topic.

Thanks for throwing some light on this.

The EPROM sockets that hold the EPROM PLA's have a 68pf capacitor on the CASRAM line as well. I am not sure whether this will alter the tests even further.

I have some other boards as well . I would be happy to test out and share the results.

I have 2 x KU style C64 boards with original functioning RAM chips, which by the way have different wiring configurations on the board. I think the CPU and Kernal ROM have been changed over in one of them. I will double check on the date codes of the other KU board.

I also think I have 2 x 250407 Artwork 251137 Rev B C64 boards. One of these has ' HiPric ' stamped on the board.

This might provide some useful insights, not sure.

[banman]

Hi eslapion,


Here are the updated videos of the EPROM based PLA solution with the corrected wiring.

C64 Board Assy No. 250425

Winbond W27C512 EPROM PLA https://youtu.be/qaRxkprkYzo


Commodore Factory PLA https://youtu.be/guNu2Fsq68w


Testing The Ultimate PLA https://youtu.be/fRqhdOY5wJw


Testing ST M27C512 90b EPROM PLA https://youtu.be/OMkxbpC0PDo

I will upload the other C64 boards soon....

[eslapion]

Testing ST M27C512 90b EPROM PLA https://youtu.be/OMkxbpC0PDo

It's a fake but it looks like it works anyways.

You should look at the photos I referenced in the previous posts.

[banman]

Hi eslapion,


I totally agree with you. I just had another look at your photos.

The photos I took of these "ST M27C512 90b" badged EPROMs and posted several posts ago look very close to the Winbond 27C512 45ns EPROMs.

I think they even ground down the old label and printed a new one on top!


On a side note, I saw this video...


https://www.youtube.com/watch?v=BA12Z7gQ4P0


It's a long watch. Towards the end of this video Ben Eater explains very convincingly how EPROMS can be used very effectively to replace multiple logic IC's.


I am not a very technically minded person.

Is this something similar to the thinking behind the Commodore PLA and their potential ability to reduce the amount of logic IC's on the C64 board?

I can see how it would have been a great space and cost saving measure for Commodore.

I know next to nothing about the original Commodore PLA construction versus the EPROM based one.

Only that timing is a very important factor as we have discovered so far.....





I appreciate your patience and willingness to further with this very interesting topic...

[eslapion]

On a side note, I saw this video...

https://www.youtube.com/watch?v=BA12Z7gQ4P0

Yes and I left the following comment:
Good thing this guy never bothered to check the output of his EEPROM with a logic analyzer. He would have noticed every time there is a change on the inputs, there is a brief period of time when all outputs are zero. This is called a static hazard. https://en.wikipedia.org/wiki/Hazard_(logic)
NEVER do what this video encourages you to do.

Is this something similar to the thinking behind the Commodore PLA and their potential ability to reduce the amount of logic IC's on the C64 board?

Only if you want this:
https://www.youtube.com/watch?v=ofg33zk9uCA&t=1840s

I can see how it would have been a great space and cost saving measure for Commodore.

It is if you have a real M27C512-90B6 but using just about every other type of EPROM, it will do what you just saw in this video.

All memory based ICs will, for a very brief period of time have all their outputs fall down to 0V when there is a change on the inputs and that's because they are not designed to be used as logic ICs. When a computer like the VIC-20 or C64 accesses a memory chip, they will first signal the address it wants to read or write on the address bus and that in turn causes the logic decode to trigger a low on the !CS or !OE or both. The selected address isn't supposed to change when this or these lines go low (in the midle of a single access cycle) because only one address is read from or written to at a time.

However, the PLA of a C64 has its inputs change all the time with the output enable staying low all the time and this means, there is NO activity break between changes in address value at the input, just like a real logic chip.

The M27C512-90B6 is the only exception that I know of and that's because is has a relatively low slew rate which filters out these glitches. This low slew rate acts as a filter which will prevent the glitches caused by this sort of 'abuse' of a memory chip from affecting the rest of the C64. In reality, if you closely examine the outputs of the M27C512-90B6 with the help of an oscilloscope, the glitches are still present but they are so significantly dampened that they can no longer represent an undesirable transition between a logic 0 and 1 when it shouldn't happen.

This is a very rare occurrence but it seems you've found one too. https://youtu.be/OMkxbpC0PDo

BTW, this is the best picture I could take of my very last M27C512-90B6. It still works fine, consumes only 8mA when working, that's about 1/3 the power of PLAnkton which is already very much power lean compared to a genuine Commodore PLA. It's the one I used at the WoC in Toronto with the Super Zaxxon cart; the one which works fine...

Genuine M27C512-90B6

The purpose of the 74LS279 circuit is to detect these static hazards without the need to use a cartridge like Super Zaxxon which happens to be very sensitive to them.

[banman]

Hi eslapion,


Great explanation, I think I am learning things.

I am going out on a limb here.....
Is this the reasoning behind why small 68pf capacitors are added (I have this added on my test EPROM socket) sometimes to the circuits of the EPROM's CASRAM line?
To try to even further slow down the slew rate. So the desired output is sloped even more (https://en.wikipedia.org/wiki/Slew_rate).

With regards to the Windbond W27C512 45ns EPROM is very close to what I am seeing on startup in this video (from MindFlareRetro)

https://www.youtube.com/watch?v=ofg33zk9uCA&t=1840s

......every thing normal. I don't have a Zaxxon Cart. However several cartridges I use show up garbled graphics and other nasty things.

I probably see about a 670 - 700ma overall power consumption testing across the 5v power supply line with the EPROM based solutions.

I see 830 -890ma overall power consumption testing across the 5v power supply line with the Commodore Factory PLA.

Thanks for providing a nice detailed image of the real thing. This will undoubtedly help in tracking down potential new supplies. I send this to sellers when I'm looking for stuff.

[banman]

Hi eslapion,


Here are some more updated videos of the EPROM based PLA solution with the corrected wiring.

C64 Boards to be tested https://youtu.be/nWfg5oE-Fzg


C64 Board Assy No. KU 14194HB Board #1

Winbond W27C512 EPROM PLA https://youtu.be/j4Xyhfq5Aj0


Commodore Factory PLA https://youtu.be/5nV343SIc0s


Testing The Ultimate PLA https://youtu.be/LPj517mWSXM


Testing ST M27C512 90b EPROM PLA https://youtu.be/Q2sqo1KpPL4

I will upload the other C64 boards soon....

[eslapion]

Is this the reasoning behind why small 68pf capacitors are added (I have this added on my test EPROM socket) sometimes to the circuits of the EPROM's CASRAM line?
To try to even further slow down the slew rate.

Nope!

The answer is here... http://sleepingelephant.com/ipw-web/bul ... 33&start=9

Testing ST M27C512 90b EPROM PLA https://youtu.be/Q2sqo1KpPL4

Interesting results. Where did you buy it ?

[banman]

Hi eslapion,


Thank you so much for that definitive answer regarding the CASRAM issue.



I somehow stumbled on someone talking on a site about PLA's and then by accident came here to this forum all totally random. I luckily have all working C64's.
I saw the descriptions of the chips you were talking about, not pictures though at that stage due to that glitch with the way the forum handled Its images.

At the same time I was looking around for 64kb EPROMS for another project. That's what those white cartridges in the test videos were for.
While browsing for Winbond W27C512 45ns EPROMs (that seems to be the goto chip people use for cartridges ) I saw the description on this sellers site for ST 27C512 - 90B6 and thought Hmmmm

If they don't work as PLA's I can re-purpose them for the cartridges I was making.
Again, I will stress I'm not very technically minded I thought the cartridge project from Sukko Perra https://www.pcbway.com/project/sharepro ... __8K_.html would be good for my abilities. He's very clear in his description.
It maybe a damm good thing I tried out 1 of these chips as a PLA first!
They are One Time Programmable and gave me some interesting results compared to the Winbond W27C512 45ns. Thankfully, that's when I started asking you questions .




I got these chips from a seller in China. I don't think he even knows what they are. I say this because the pictures on the site are not the same as what he sold me.


I have been talking with him, however it is challenging with a language barrier issue.
This is what I can gather from our communications....

He has 300+ items on hand. He may be able to lay his hands on more!


By the way elsapion, are there any other chips that may be similar to M27C512-90B6 in characteristics? For example the 90ns speed characteristic.

The reason I say this is because I like to shop around online. There has to be other undiscovered sources.
If you give me a shopping list of key features to look out for I would be happy to buy and test samples, 90ns speed, windowed or non windowed,OTP....that sort of thing. I know it's a bit broad and vague. A few clues is all I need .



I would like to upload the rest of these test videos for you and others to look at them so that I am absolutely accurately reporting what could be something worthwhile (by the way please don't hesitate to tell me to stop uploading more test videos if you think we have a satisfactory candidate).


I know you will agree due diligence is paramount here.

[banman]

Here are some more updated videos of the EPROM based PLA solution with the corrected wiring.




C64 Board Assy No. KU 14194HB Board #2


Commodore Factory PLA https://youtu.be/CfOsfLE02zU


Testing The Ultimate PLA https://youtu.be/4jxN0SiXJrU


Testing ST M27C512 90b EPROM PLA https://youtu.be/aGYbMAjLsDk

I will upload the other C64 boards soon....

[eslapion]

By the way elsapion, are there any other chips that may be similar to M27C512-90B6 in characteristics? For example the 90ns speed characteristic.

The speed is totally unimportant when it comes to using a memory chip as a logic chip. What really matters is the low slew rate which acts as a spurious transitions filter. This is not something you can ever find in the datasheet of the products. The only way to know is to test them one at a time.

The alternative is to create your own filter and that's something Ray Carlsen has achieved. This guy also happens to be the only person I know which has a few genuine M27C512-90B6 in stock.

If you look at the market for brand new 64kx8 bits PROMs on the market, there is Winbond which is mostly only from Chinese vendors and there is Microchip's (formerly Atmel) AT27C512R and that's pretty much all. Mouser and Digikey only sell this last one.

There is probably dozens of flash parallel memory chips which could also do the job but there too, it's a matter of checking them one at a time. If you're going to engage in this sort of exercise then it's much better to get yourself an oscilloscope and do a thorough job than just checking with a simple 74LS279 IC.

For anyone else not interested in doing what amounts to a tedious monk's job, I make and sell PLAnkton for 15.50$US/13 Euros each!

[banman]

Hi eslapion,


Excellent!

Good to know you sell replacement PLA's.


Here are the updated videos of the EPROM based PLA solution with the corrected wiring.


C64 Board Assy No. 250407 REV A Testing



Winbond W27C512 EPROM PLA https://youtu.be/nH92jWReWzs



Testing the Commodore Factory PLA & Testing ST M27C512 90b EPROM PLA https://youtu.be/xlcMXUJrbvQ



I will upload the other C64 boards soon....

[banman]

Hi eslapion,


Here are some more updated videos of the EPROM based PLA solution with the corrected wiring.




C64 Board Assy No. 250407 REV B Testing


Commodore Factory PLA https://youtu.be/9drT57Lm3Ms



Testing Winbond W27C512 EPROM PLA https://youtu.be/6VSVH0xAetw

Testing Winbond W27C512 EPROM PLA with PACMAN cartridge https://youtu.be/a61GC_yb_2g

The Winbond chip is unusual under this test. I believe it passes the test. However when a PACMAN game cartridge is played it definately fails the test. This is no doubt due to me not letting the test run on for long enough for a light to show on the test circuit .


Testing ST M27C512 90b EPROM PLA https://youtu.be/33cA1WOoPkg



I will upload the last C64 board soon....

[eslapion]

There's not much point doing all these tests.

If a memory chip used as PLA subsitute pops the LED back on when used on one board then it generates glitches and it will do it on all boards.

If the LED stays off after the initial power up and resetting then it will do the same with all boards.