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

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

Post by eslapion » Thu Aug 01, 2019 6:22 am

Wow! What a stockpile! These sockets are worth money!
banman wrote:
Wed Jul 31, 2019 9:28 am
There is a varied selection of what I strongly believe are original 27512 EPROMs.

This will provide a good test reference for checking out the Glitch when I manage to get the oscilloscope up and running....

I think having a genuine ST 27C512 very similar to yours on hand will be a benefit when comparative testing on the same oscilloscope is run against the newer Knockoffs (fake) ST 27C512 90B1..B6's..FX1 from China.

My way of thinking is even if the oscilloscope isn't dead actuate at least all the results will out by the same margin. That is my guess anyway.....
I can't read the whole code on your photos so I don't know the speed code for most of the ST PROMs you have in there. I can tell you -15B6 means 150ns so these are much too slow to be used as PLAs.

They do have the correct form factor and country of origin.


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

Post by banman » Thu Aug 01, 2019 6:52 am

HI eslapion,

Thank you for the information about the meaning on the ST PROM ..15B6 being 150 ns.... I just checked them unfortunately the 4 are 150ns speed.


Damn... I thought I had a similar ST PROM to yours ..

They do look striking like your ST PROMs in printed and physical markings. That's what got my attention..

The windowed ST EPROMs in that same photo are ST M27C512 10F1. Would that be 100ns speed?

I understand that the slower E/PROM speeds would not be suitable as a working PLA substitute. With these slower E/PROMs do you think that the Glitch will still be present in a similar way that the ST M27C512-B6 running at 90ns on C64 start up?

Maybe not a loss after all. These may make good oscilloscope comparative test subjects to observe glitches....



Not to worry.... I will go thru what I have and document the E/PROMs for future reference. There is a lot to sort thru.

Basically it was like buy a full box and take your chances....

The turned socket holders look like good quality. I think they are made by Thomas & Betts...There is more still at the shop.....

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

Post by banman » Thu Aug 01, 2019 9:03 am

Hi eslapion,


I was just brainstorming....


Maybe I am looking at this the wrong way.

Would it be possible to make a stand alone circuit that would trigger an E/PROM in such a way that we could observe the output on an oscilloscope (i.e. the Glitch)?

I would be more than happy to give building the circuit a go. :)

I know it is not the spirit of this thread which is focused on the C64 PLA E/PROM substitute.

It would give a wider net to test different manufacturers who no doubt use different fabrication processes and circuit designs.

I have a good range of E/PROMs now....


My suspicion lies in the circuit design of ST E/PROMs whether they are original or knockoff (fake). I could be wrong . In fact I'd very much like to be proven wrong.

I think further observations with the oscilloscope is essential.

Just a thought....

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

Post by eslapion » Thu Aug 08, 2019 5:10 pm

banman wrote:
Thu Aug 01, 2019 9:03 am
Would it be possible to make a stand alone circuit that would trigger an E/PROM in such a way that we could observe the output on an oscilloscope (i.e. the Glitch)?
That's not as easy as it sounds. The reason why a glitch on outputs will appear depends on a combination of things.

The first one is there was an address change while the !CS !OE! both remained low - when a CPU reads data normally, one of the two will go high between each access, not so when using a memory chip as a logic chip. The second one depends on what the values are at both the initial address and the new one. It can also depend on the selected addresses themselves as the EPROM could temporarily 'see' an address where the stored value is 00 or any value that is 'equivalent' to a glitch. Finally, the fundamental electronics of the EPROM, for which the manufacturer will not provide a schematic is at play.

The C64 itself and the truth table of the PLA appear to be an ideal circuit for determining the presence of spurious logic low in the output. In other circumstances, there may be spurious logic highs as well but these are not an issue when it comes to using an EPROM as a PLA in a C64.

Sidenote:
If you happened to have found some of those super low profile Robinson-Nugent sockets with 40 or 48 pins in your recent find, I would be interested in buying.

Any 48 pins sockets with machined pins could be of interest too.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman » Sat Aug 10, 2019 10:53 am

Hi eslapion,

Thank you for the clear explanation on the reasons for not creating a simple standalone circuit for testing the C64 PLA. :-)


Absolutely regarding the ic sockets. :-)

I will look out for them.

I have come across some sockets that have super long legs on them.

I plan to go back on Monday to have another look. There is more stuff to come up from the service centre.

I have seen an old BK Precision digital counter and a BWD (I think they might be made in Melbourne) sine wave generator that might be handy to have as a beginner.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by eslapion » Sun Aug 11, 2019 7:43 am

banman wrote:
Sat Aug 10, 2019 10:53 am
I have come across some sockets that have super long legs on them.
It's wire wrapping sockets.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by eslapion » Sun Sep 15, 2019 8:29 pm

As I often mentioned in the past, the Sega Super Zaxxon CARTRIDGE is a very good way to check if a PLA generates glitches on the C64.

Now, the real cartridge is becoming a bit of a rarity and it's more complex than most carts because it uses logic ICs to toggle access to a specific part of the ROM. Fortunately, there are people making clones of the cart which are a bit modified but still use the same access scheme, same logic ICs.

I found this on eBay:
https://www.ebay.ca/itm/Commodore-64-12 ... 2775042281

Looks like it's gold plated on the connector so it's safe for your cart port connector.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman » Tue Sep 17, 2019 6:41 am

Hi eslapion,

Apologies for not posting for a while. Things got busy between work and checking on the electronics store.

That is interesting about the Super Zaxxon cartridge. I was having trouble tracking down an original. I didn't think to look at replicas, I will look into that. Thank you...


Sadly, the electronics store closed on the 13th September. :cry:

I did manage to get a hold of some interesting things.

While this was transpiring I managed to cobble together a few Swinsid replicas using parts from the electronics store.

Interestingly some of the crystal oscillators I used were dated 1989. They seemed to work fine.

Check out the YouTube video below.....


20120629_135342 Assembled SwinSid nanos.jpg
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I picked up a B & K 80's vintage frequency counter & sign wave / square wave generator as well.

There were heaps of early 70's 74xxx series chips as well.


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I got as much sockets as I could. 3 boxes of 38pin turned sockets. Various other sockets (see the pictures). Let me know if any suits your needs.


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I a tried to get as much of the chips that a C64/C16 uses (all various OEM new old stock). I missed out on 74LS258, MC4044, LM556. I think I got some 74LS628 (C64 used 74LS629) not too sure if these are compatible or not.


I quite by accident found a suitable battery for the oscilloscope on the last day, the 13th. I still have one on order from China. I had to extend the shipping time. It's taking for ever.

The old battery is a "Keeper" brand dated 1987... Completely flat, however no leakage whatsoever ...

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I have the Oscilloscope stripped down. I just cut the leads of the old battery. I will take care when replacing the new battery, I will make sure the polarity is right and everything is grounded.

Say a prayer for me! :)

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

Post by banman » Tue Sep 17, 2019 7:15 am

Hi eslapion


Some of these oscillators in the Swinsid's date as far back as 1989 (I would say with a high degree of accuracy that they were all from the late 80's).

They look like they have never been used at all. They seem to play fine (see the YouTube video ). A 32mhz crystal oscillator was what the circuit design requested. It will work down to about 20Mhz according to some web sites. I have 24Mhz oscillators though I haven't had a chance to test this out yet.
I read somewhere that it has something to do with the speed at which the Swinsid can effectively utilize. 20Mhz is the lower setting. I did try a 40 Mhz in the socket. It does not play well at all (see the video).
I have tried a few cartridge games and the sound seems to play ok. These Swinsid replicas have the Lazy Jones fix applied to the firmware. I noticed one YouTube site put a delay capacitor on the CASRAM to fix an issue with the Aliens game missing some voices on the intro music.

I wonder how these Swinsid's will behave if I revert them back to stock firmware and test them on Lazy Jones and Aliens with the E/PROM based substitute?? ;)


By the way what is effect of this type of prolonged aging on the crystal? Do they just settle down after awhile? Everything seems to play fine here.

I noticed the the C64 is drawing about 600ma from the 5v line with an E/PROM based solution and a Swinsid replica . The only thing that gets hot now is the VIC II chip.....

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

Post by banman » Tue Sep 17, 2019 7:33 am

Hi eslapion,


What are these?


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These look like chips without anything on them...... :?:


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