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

[banman]

Hi Mike,

Thank you very much for clearing that up. Much appreciated for the information.



Hi eslapion,


I was looking at a write up on hackup.net and viewed this video. Very interesting!


https://m.youtube.com/watch?v=p0r158FDf ... e=youtu.be


My internet connection is a bit dodgy and I have trouble making out some of the component connections this video.

I found this video (yours I believe) which has the schematic if anyone's interested in making one.

(after 17:46):

https://www.youtube.com/watch?v=ofg33zk9uCA


Here is a screenshot of what I think is the schematic to test for a glitch on an eprom pla.


I have ordered some parts to build this. It will most likely take a few weeks for the parts to arrive.

Can you confirm this is correct please eslapion.

If you have any comments or suggestions I would be greatly appreciative.

[eslapion]

I found this video (yours I believe) which has the schematic if anyone's interested in making one.

(after 17:46):

https://www.youtube.com/watch?v=ofg33zk9uCA


Here is a screenshot of what I think is the schematic to test for a glitch on an eprom pla.


I have ordered some parts to build this. It will most likely take a few weeks for the parts to arrive.

Can you confirm this is correct please eslapion.

It's not my video at all, this is a video of me at WoC in December 2017 and the schematic is correct.

Credits for the video go to MindFlareRetro.

[banman]

Hi eslapion,

Great, thanks for that information.

Most Informative.

Let's wait and see what I discover about these chips...

[eslapion]

Hi eslapion,

Great, thanks for that information.

Most Informative.

Let's wait and see what I discover about these chips...

Remember the explanations in the video: The C64 will check for the presence of a cart at power up and this will turn on the LED.

If you reset it and then it turns back on then the PLA generates glitches.

[banman]

Hi eslapion,


Thank you for that extra important information.

This will help me perform the correct test procedure.

[banman]

Hi eslapion,

Apologies for not posting earlier. Work's been frantic and Easter was a busy time for me.


The parts arrived and I have made the test circuit up.


Before we continue this discussion.....

Could you please look at the pictures I have uploaded to check that I have indeed constructed your Eprom PLA test circuit correctly? Thanks



I used an existing 8kb ROM cartridge circuit to take off the 5v and GRN as well as ROM hi and ROM lo. They can be seen in the pictures printed on the circuit board. I checked these against a wiring diagram for the C64 expansion port and appear to be correct.

I found this to be useful as I am not a skilled person by any means.

The Red/Brown wire goes from ROM lo to Pin 11 on the 74LS279 IC breadboard.

The Yellow/Black wire goes from ROM hi to Pin 12 on the 74LS279 IC breadboard.

Pin 10 runs thru the switch to Ground.

Pin 9 goes thru a 500 ohm resistor and LED to Ground.

Pin 8 is Ground.

Pin 16 is 5v.


There is a whole bunch of resistors at one end of the breadboard. They serve no purpose to the circuit and are not connected.

I just used it a place to park them so I wouldn't misplace them.

My construction skills are not very good.

I need to make sure that what I am reporting is accurate to the best of my abilities.

If you think I have it right I will upload videos of 3 different PLA's . Very interesting!

[eslapion]

The IC is correct but concerning your request of me checking your connections, all I see is a bundle of wires. I cannot use a continuity tester on your photos!

Me, when I did that test circuit, I soldered the tiny pushbutton, resistor and LED directly to the 74LS279 and used 4 very small alligator clips to the cartridge port connector leads. This requires opening the case and no actual cartridge board.

Also, if you use a 500 Ohms resistor, the LED will be dim and probably quite difficult to see when it lights up.

[banman]

How very true you you are!

I have gone over the circuit I made numerous times to make sure I have it correct to your schematic.

The LED is visible but not super bright as you predicted.

Here are some youtube links to some videos I took recently regarding the EPROM based PLA solution



https://www.youtube.com/watch?v=cMzcvTi ... e=youtu.be

https://www.youtube.com/watch?v=LaBf4N3 ... e=youtu.be

https://www.youtube.com/watch?v=fRx9tTq ... e=youtu.be

https://www.youtube.com/watch?v=_jODPG_ ... e=youtu.be




I have made some more longer ones with different board revisions.

I will upload these if I haven't already bored the pants off you with my home movies.. Ha.....

{EDITED: 1047pm 22/05/2019 : All the above YouTube videos are giving false results due to incorrect wiring}

[eslapion]

There is a serious problem with 3 out of 4 of your videos.

If the LED doesn't turn on when you power up your C64 then your test circuit is faulty.

Only the first one is a valid test.

[banman]

Hi eslapion,


Yes, you're right! I can't believe I made such a simple mistake in the wiring.

I will say that ALL of the above videos I posted above are giving wrong results.

Remember the explanations in the video: The C64 will check for the presence of a cart at power up and this will turn on the LED.

If you reset it and then it turns back on then the PLA generates glitches.

The problem isn't on the breadboard. It is on the cartridge PCB.

After looking through Sukko Perra'a extensive documentation.


https://github.com/SukkoPera/OpenC64Cart


I had neglected to the close EXEROM jumper pins. Without it the ROM hi and ROM lo lines won't operate correctly.

I have remedied this silly error, and will upload videos with the updated wiring.





Thank you for your help and patience in this.

[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...