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

[eslapion]

I hooked up my logic probe to a !ROML take off along side the Texas Instruments 74LS279 Quad S-R Latch I have installed in eslapions's circuit and noticed that I could detect the glitches in TTL mode and CMOS mode.

Very good idea.

In TTL mode it seems to trigger more with a known bad Winbond EEPROM PLA substitute than the Texas Instruments 74LS279 Quad S-R Latch I have installed in eslapion's circuit. No doubt due to the Texas Instruments 74LS279 Quad S-R Latch's characteristics. Actually the logic probe flashes quite a bit.

All I can imagine is the images on your oscilloscope and the wave forms that were produced on the incompatible PLA.

I would assume the threshold level of your prove in TTL mode is slightly different from the actual 74LS279. Probably 1.5V for the probe and 1.3V for the logic chip.

In TTL mode no triggering occurs with the knockoff (fake ST M27C512-90B6) PLA substitute and the Commodore Factory PLA.

However, in CMOS mode every PLA tested pulses.....

Even the Commodore factory PLA pulsed in CMOS mode as much as the PLA substitutes....

Then this probably means the threshold level of your probe in CMOS mode is too high.

[banman]

Hi eslapion,


Thank you for all the patience you have given me.

I honestly would not have thought to use the Logic probe. It is only all the conversations we have had made me twig maybe a logic probe would be a way of getting around the issue of using suspect M74HC279 CMOS chips.

Having the TTL threshold level on the high side is probably a good thing in picking up on the voltage glitches.


I agree the CMOS function seems a little too sensitive.

Any suggestions on a damping circuit to drop the levels down a touch?

It doesn't have to be much and I would say it is only going to be used as an indicator. Not any bona fide scientific measurements or such.


I got the delivery of the 'infamous' ST M27C512-90B1 OTP made in CHINA PROMS today.

I won't get time to do much with them for a day or so.

I did take some photos. I noticed that the strip containers had wear marks on the inside where the chips had been moving back and forth in shipping.

This can be evidenced on the surface of the chips themselves (see the photos).

There seems no evidence of 3rd party doctoring that I can tell. Every thing seems as if it has come straight from the manufacturing plant.


I am very interested to see how these work out.

I have a suspicion about all these chips.


Thanks again eslapion for giving me the idea to use the Logic probe....

[eslapion]

I honestly would not have thought to use the Logic probe. It is only all the conversations we have had made me twig maybe a logic probe would be a way of getting around the issue of using suspect M74HC279 CMOS chips.

Having the TTL threshold level on the high side is probably a good thing in picking up on the voltage glitches.

Yeah but it's probably more useful if you have some way of measuring at exactly what voltage your probe considers the TTL signal to be low.

I agree the CMOS function seems a little too sensitive.

Any suggestions on a damping circuit to drop the levels down a touch?

You can't 'pump-up' a signal to match the threshold level of the CMOS mode of your probe but you could bring it down to the threshold level of the TTL mode so a simple voltage divider made using a pair of resistors or 1k Ohms potentiometre wiper could do.

To do that, you need, as indicated above, to check what the exact threshold level of your probe is.

I got the delivery of the 'infamous' ST M27C512-90B1 OTP made in CHINA PROMS today.
...

There seems no evidence of 3rd party doctoring that I can tell. Every thing seems as if it has come straight from the manufacturing plant.

The ink/dye on the branding/etching is way too contrasted to be from any genuine IC manufacturer.

The IC strips are packaged with ordinary food grade cellophane. Buy anything from an authorized distributor like DigiKey or Mouser and you'll see the packaging is much more professional. You would normally receive your ICs inside an antistatic bag. https://en.wikipedia.org/wiki/Antistatic_bag

Thanks again eslapion for giving me the idea to use the Logic probe....

Who ? Me ? If you say so...

Forgot to ask: what is the make/model of your logic probe ? There is one in my Meterman 37XR.

Added edit: I sent you a PM a few days ago and you didn't read it.

[banman]

Hi eslapion,



The probe I have is a very cheap one. I do not think it even has a brand name.

Here is a link to one like it

https://www.aliexpress.com/item/OOTDTY- ... st=ae803_3



I will check out Meterman 37XR digital multimeter.

You can't 'pump-up' a signal to match the threshold level of the CMOS mode of your probe but you could bring it down to the threshold level of the TTL mode so a simple voltage divider made using a pair of resistors or 1k Ohms potentiometre wiper could do.

To do that, you need, as indicated above, to check what the exact threshold level of your probe is.

Thank you. I am looking into it now....

[eslapion]

I will check out Meterman 37XR digital multimeter.

The indispensable tools of all electronic workbench:

- a good multimeter
- a soldering iron
- a lab power supply with controls for both voltage and amps
- a function generator
- an oscilloscope

[banman]

Hi eslapion,


Very good advice....


Thank you.....

[banman]

Update.....

Here are some links to videos I made recently testing various PLA's including a NEWLY DISCOVERED Knockoff (fake) ST M27C512-90B1 manufactured in CHINA OTP PROM on a C64 Board Assy No. 250425 board revision that appears to pass eslapion's test circuit.

These are knockoff (fake) Made in CHINA ST M27C512-90B1 OTP PROMS .

****************************************************C64 Board Assy No. 250425***************************************



Winbond W27C512 EPROM PLA


I am not sure if this is displaying bus contentions or not.



https://youtu.be/OORQERyNuw4




Testing The Ultimate PLA


https://youtu.be/wf7hOEQwU14





Testing Knockoff ST M27C512 90B1 manufactured in CHINA PROM PLA substitute.



https://youtu.be/TQGKhfToT2w

Note how the Winbond W27C512 EPROM PLA behaves erratically in the videos....

[levoman]

This is my first post here , so please excuse any 'dumbness' on my part , not about the computers but about the forums.

has anybody tried the bios style 32 pin rams with this . The 010 70ns or the 004 33ns ram . Just tying the unused lines high?

[levoman]

sorry i meant flash rom of course!

[Mike]

This is my first post here , so please excuse any 'dumbness' on my part , not about the computers but about the forums. has anybody tried the bios style 32 pin rams with this . The 010 70ns or the 004 33ns ram . Just tying the unused lines high? [...] sorry i meant flash rom of course!

A 32-pin PLCC chip can 'easily' be fit on an adapter PCB that sits on two pin rows 600 mil apart, similar to what you see here: (link).

Main issue remains that only a few types of EPROMs will work reliably as PLA replacement in a C64, regardless which package type it is.

[levoman]

So the only use is for a swap test for pla or to use for emergency only!

[eslapion]

So the only use is for a swap test for pla or to use for emergency only!

There are ways to check if a memory chip can be used to replace the Commodore PLA. The Super Zaxxon cartridge is very sensitive to glitches. And I posted the schematic of a circuit which uses a 74LS279.

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

Detailed thread with scope captures: http://www.melon64.com/forum/viewtopic.php?f=12&t=8691

[levoman]

Since the super zaxxon is hard to get hold of and i have a limited number of cartridges in my collection are there any other cartridges that display symptoms? There are a number of cartridges that have this bank switching. Here are a few from my collection.

[eslapion]

Since the super zaxxon is hard to get hold of and i have a limited number of cartridges in my collection are there any other cartridges that display symptoms? There are a number of cartridges that have this bank switching. Here are a few from my collection.

None of these use a flip-flop (74LS74) to toggle access to a different range of address in a (EP)ROM so none of these will have a sensitivity to noise in the PLA signals /ROML and /ROMH.

Only Super Zaxxon or a clone of it will do. Jaystonian sold a few clones on eBay and they use the same trick with exactly the same chip. Besides, IMHO the cartridge version of Super Zaxxon is much better than the disk version.

Noteworthy: Some people have used the .CRT version of Super Zaxxon cart on Easyflash. Well, easy flash is not equipped with a flip-flop and emulates that function in a completely different manner so using Easyflash also will NOT do.

See:
https://www.hackup.net/2018/10/super-zaxxon-replica/

[levoman]

Burnt an eprom , just need to build a cartridge. Anybody know of a pcb available or do i have to do my own?