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

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

Post by banman » Mon Jul 01, 2019 11:25 am

Hi eslapion and radron5809


This is where I got mine :



https://www.aliexpress.com/item/3270864 ... 17edd4kd9b








eslapion wrote:
Mon Jul 01, 2019 10:16 am
Using a 74LS279 as a means of detecting undesirable spurious logic lows from a PLA will allow you to tell for sure if a PLA has problems but the opposite is not true. If a PLA will not trigger the test schematic I have suggested then it MAY be a good PLA replacement but using an oscilloscope, as I did is the only way to be perfectly sure.

The Rigol DS1052E is probably one of the least expensive scope you can get which will do the job but there are many others that may be even less expensive.
I absolutely agree. :D


Here are some updated videos using the Motorola 27LS279 chip installed.


Knockoff (Fake) ST 27C512 - 90B1 (ST electornics never relaesed a ...B1 variant!)






Commodore Factory PLA







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

Post by banman » Fri Jul 05, 2019 2:49 am

Hi eslapion,



I picked up from the same old electronics store near me 3 UV erasable PROMS.

1 x Fairchild B0218AD FM 27C512Q 90 and 2 x ST 27C512 - 90F1 manufactured in Singapore.

20120413_151310.jpg
20120416_122609.jpg
20120413_151337.jpg


I have tested the Fairchild B0218AD FM 27C512Q 90 UV erasable PROM. This EPROM looks OK until one starts taping on the key board. Random colors then start to come on to the typed text. So I would say this is not a good PLA substitute.




I initially tested the 2 x ST 27C512 - 90F1 manufactured in Singapore UV erasable PROMs.

One programmed alright and verified ok in the programmer. However when I used it in the C64 board it would come up a grey screen only. Not the usual C64 startup screen.


The other ST 27C512 - 90F1 manufactured in Singapore UV erasable PROM didn't seem to want to program at all. I tried to program it several times. I also used several lengths of time in the UV eraser.


Only by chance I adjusted the the Pulse Delay to 500us from the factory setting of 100us. I had Blank check off, verify off and skip 0xff off. Every other setting else I left alone.
This time it worked OK.
Image


I tried it twice more and verified manually to make sure it was doing it right. The TL866 programmer would some times tell me that the chip wasn't making good pin contact before the start of the programming cycle. I would just keep retiring till the procedure started off. After the programming started it didn't seem to halt on a error.


The ST 27C512 - 90F1 manufactured in Singapore UV erasable PROM that wasn't programming correctly now did.

I now tried this chip in the C64. It seems to work fine! It passes eslapions test circuit and Game cartridges play OK.

I can't seem to find any Issues as yet. Though an oscilloscope would be need to do further checks.


I then proceeded to reprogram the first ST 27C512 - 90F1 manufactured in Singapore UV erasable PROM that gave me the grey screen on C64 startup. This time I now used the adjusted setting of 500us (remember that this first chip programmed and verified ok at 100us)

I verified manually to make sure it was right. I had Blank check off, verify off and skip 0xff off. Every other setting else I left alone. The TL866 programmer would some times tell me that the chip wasn't making good pin contact before the start of the programming cycle. I would just keep retiring till the procedure started off. After the programming started it didn't seem to halt on a error. It did take 5 times longer to program the chip than on 100us.



I tried this first chip back in the C64 and it works as well! It seems to work fine. It passes eslapions test circuit and Game cartridges play OK as well.
Image


I will upload videos time permitting.



I am not sure as to why this is.

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

Post by eslapion » Fri Jul 05, 2019 3:24 am

The ST EPROMs seem genuine.

Concerning your programming problems, all ST PROMs have their own programming algorithm. If you try to use a generic programming mode then you have to use the old slow 'harsh' method.
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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman » Fri Jul 05, 2019 3:32 am

Hi eslapion,



Thank you for that information regarding the programming of the ST PROMS. :D

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

Post by banman » Fri Jul 05, 2019 5:31 am

Hi eslapion,


I got a call from the old electronic store that is closing down.

He says he has an old Tektronix 2430A digital oscilloscope for $250AU. It came up from the service dept.

He says it fires up and goes thru a self check but that it comes up with errors. He hasn't noted them down so I am not sure what they are.

I did a quick search and it seems common fault is a failing memory backup battery which gives a "fail 4000 FPPP" error code on startup. I can change out a battery.

Assuming that the problems are not catastrophic with this unit would it be suitable for my PLA testing needs?


I appreciate all you assistance.... :D

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

Post by eslapion » Sat Jul 06, 2019 8:48 am

banman wrote:
Fri Jul 05, 2019 5:31 am
He says he has an old Tektronix 2430A digital oscilloscope for $250AU. It came up from the service dept.

He says it fires up and goes thru a self check but that it comes up with errors. He hasn't noted them down so I am not sure what they are.

I did a quick search and it seems common fault is a failing memory backup battery which gives a "fail 4000 FPPP" error code on startup. I can change out a battery.
A lot of people look at old scopes and see a potentially good deal because they are outdated but it can be a real mistake.

Old scopes, if they are in excellent condition or easy to fix can gain monetary value because they can be classics of more or less value. You pay extra only for the museum effect. Don't think that's something you want here.

I looked up the 2430A and I wouldn't even know how to use it properly or get measurements out of it. It's also incredibly heavy and power hungry. A massive beast. Impressive looking set of buttons and dials I wouldn't know what to do with because good scopes are much more automated.

You can probably get a small scope that's much easier to use and weigh less than half as much for the same price or less with nothing to fix.

Avoid historical scopes unless you know oscilloscopes very well. They are like flying ancient aircrafts - impressive vintage look, much more dials to dabble with since everything is manual. Very few people around to help you.

Compare the 2430A with a TDS210. The TDS210 looks like an innocent toy comparatively but you can really get a lot more out of the TDS210 and it might be cheaper. The same is true of the more recent TDS1002.
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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Re: The Dos and Don'ts of using an EPROM as PLA in a C64.

Post by banman » Sun Jul 07, 2019 9:59 am

Hi eslapion,


You are right, it looks like a big one..... :shock:


It must have been one of the early digital oscilloscopes on the market.


I actually haven't had the time time to go down to look at it. I have got the flu currently and I didn't want to pass it on..

I will probably go on Tuesday and have a chat. The man at the shop was kind enough to phone me initially It would no doubt have gone by then.... :D

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

Post by eslapion » Mon Jul 08, 2019 8:14 am

If it's more complicated to use than what you see in this video then I suggest you stay away from it.

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

Post by eslapion » Fri Jul 12, 2019 9:51 am

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

Post by banman » Sat Jul 13, 2019 3:19 am

Hi eslapion,



Thank you for the videos on selecting an oscilloscope. I think I will buy one of these newer style units. They have more capabilities than the older ones.



I went down to the electronics store and saw the oscilloscope.

It truly was a beautifully made machine. I managed to get it for $150 AUD. Cosmetically, it is in mint condition, nothing broken scratched or missing. It has a small vinyl storage pouch on the top. There doesn't appear to be any phosphor burn in on the tube.

It has a very detailed user manual in great condition and it has detailed service records where it was serviced at the Australian Tektronics service center. A real find!

It comes up with errors. I did some online research and it seems to point to the fact that the battery backup is flat.
A new battery should help keep the calibration data going when the machine is off. A self calibration run should clear up some of the errors. I think an external one is required with a bench power supply.


I opened it up and I clipped the battery off the PCB. Fairly easy, there was a later model that used RAM chips with the battery potted on to it (Dallas DS1235 32Kx8 NVRAM module).

I ordered a newer contemporary part a 1/2AA size lithium thionyl chloride cylindrical 14250 battery, 3.6V high energy battery with soldering pins. Saft brand. Capacity: 1200mAh slightly lower than the original. It should be here in a few weeks.

I will let you know how it goes.....




Yesterday I got a delivery from China of 8 pairs of various 27C512 E/E/PROMS.

I haven't had the time to check all the chips.


This chip passes eslapion's PLA test circuit. It is a knockoff (fake),

Interestingly , I took some comparison photos of these chips with the genuine ST 27C512-90F1 from the electronics store.

Notice that the knockoff (fake) chips have a different manufacturing process to the genuine one. The genuine die is maybe 2-3 times smaller that the knockoff (fake) ones.


ST 27C512-90F1 B88AY 9605C SINGAPORE knockoff UV EPROM.

Genuine ST 27C512-90F1 vs ST 27C512-90F1 B88AY 9605C SINGAPORE knockoff
DSCF4047Genuine ST 27C512-90F1 vs ST 27C512-90F1 B88AY 9605C SINGAPORE knockoff.JPG


Genuine ST 27C512-90F1 vs ST 27C512-90F1 B88AY 9605C SINGAPORE knockoff
DSCF4046Genuine ST 27C512-90F1 vs ST 27C512-90F1 B88AY 9605C SINGAPORE knockoff.JPG
ST 27C512-90F6 5880X 9806E SINGAPORE knockoff vs Genuine ST 27C512-90F1
DSCF4044ST 27C512-90F6 5880X 9806E SINGAPORE knockoff vs Genuine ST 27C512-90F1.JPG
Last edited by banman on Sat Jul 13, 2019 3:32 am, edited 2 times in total.

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