Another one thinks the earth is flat...

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eslapion
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Another one thinks the earth is flat...

Post by eslapion » Tue Feb 23, 2016 6:32 am

Another hole-in-one from Tynemouth Software, on their blog, november 2015.

Beware if you're too sensitive to gross factual disinformation... this may not be for you.
http://blog.tynemouthsoftware.co.uk/201 ... ments.html

I had to e-mail these guys but nothing moved...

"On your blog you posted the following information concerning C64 PLAs and potential substitutes:

"There are a few designs around using CPLDs, but most of the 5V ones have been discontinued, so they would need 3.3V to 5V level shifters on the outputs."

I can assure you this is absolutely not the case.

Genuine Commodore made PLAs use NMOS technology. As such they can only signal from 0v to Vcc-1v in best cases. Also, the C64 itself also use NMOS or TTL-LS technology which can also normally only signal 0v to Vcc-1v and has a logic threshold of approx 1.3 volts.

Thomas 'Skoe' Giesel, the creator of Easy Flash and Easy Flash 3 has measured the actual output levels of Commodore PLAs to about 3.7 volts at the most. He published his detailed findings in this document:
http://www.zimmers.net/anonftp/pub/cbm/ ... sected.pdf

Last august, me and Fredric Blaholtz have created PLAnkton, a substitute for the C64 which uses the Xilinx XC9536XL CPLD and we run it at the highest recommended voltage of 3.6Volts. This chip is 5V input tolerant but running it at 3.6volts provides the highest possible compatibility. It provides the same level of compatibility as a genuine Commodore made PLA.
Find information here:
http://www.amibay.com/showthread.php?77 ... ch-is-here!


Actually, using a PLA replacement which signals at a full rail-to-rail or 0-5V can cause problems if the power supply is providing ever so slightly more than 5V. Some cartridges don't like that at all, the Super Snapshot V3 and V4 are among them.

You also posted this which is also false:
"Timing seems to be an issue, only certain EPROMs seem to work at the right speed, the Atmel AT27C512R-45PU (450nS) being a good choice."

In the past, I used to produce PLAkate, the only PROM based PLA which did not require any adaptation to run directly on a C64 board and provide 100% compatibility. However, because of its low CASRAM latency, it would only operate properly on board 250466, 250425 and the SX-64 because they provide a RC filter on CASRAM (R42 and C204). It used the ST M27C512-90B6 which is now discontinued - circuits sold on eBay with this part no. are actually fakes from china and do NOT have the same properties as the original.

All other PROM circuits, including the Atmel AT27C512R which I saw in your photos will cause glitches when a "don't care" change on input occurs. A "don't care" change is when a change occurs on input which should not cause any change on the output; a PROM still must lookup its table of values to find the new output and this causes all outputs to go low for a brief period of time. This signals multiple circuits to talk on the data bus at the same time and a bus contention occurs.

Using the Super Zaxxon cartridge reveals the problems caused by these spurious glitches. I also published a small simple circuit using a 74LS279 on Amibay and Denial.

You can filter the glitches cause by the Atmel PROM in a manner I described on the REMOVED forum by putting a resistor on ALL 8 OUTPUTS. This was experimented by Ray Carlsen.

I can provide you with detailed technical information as to why the ST PROM works fine and the Atmel will cause problems if you want me to. It has very little to do with CASRAM latency."


I forgot to mention the part where it says 450ns...


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Re: Another one thinks the earth is flat...

Post by MarcWalters » Wed Feb 24, 2016 4:35 am

There's acknowledgement of PLAnkton in the blog's comments section.

Communication and dissemination of technical information, especially in the hobby/amateur arenas, is prone to lag and omission due to higher priorities of those involved (jobs, personal life, etc). Perhaps the blogger intended to base a future entry on your information rather than just an update, or was just waiting for time to do the new information "justice". Regardless, the reference to "gross factual disinformation" seems rather assumptive. And no matter which way it is viewed, the situation with online information is far better than the old days when it took a minimum of two or three months for corrections to appear in the old paper-based monthly journals.

A product such as PLAnkton will succeed in the long term due to "word of mouth" from satisfied users, and evaluations of its inherent qualities. Short-term problems such as skepticism and resistance due to subjective human traits and "filters" are normal and of no consequence in the long term. To react negatively to such events is pointless.

As an aside, I have been following the development and discussion of the PLAnkton for some time now, and will order some in the near future. Keep up the good work, guys!

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Re: Another one thinks the earth is flat...

Post by eslapion » Wed Feb 24, 2016 6:41 am

@MarcWalters
This thread is not about PLAnkton at all.

I find it very worrisome that somebody who sells antique computer services and products, somebody who is regarded publicly as technically competent would make such grossly erroneous claims.

There are ways to use a PROM as a reliable PLA on the C64 and this was extensively discussed. Even with the glitches caused by the Atmel AT27C512R-45, there are ways to use it as a reliable PLA on the C64. This was discussed on other forums and Ray Carlsen does it regularly.

Somebody with the technical know how can pay much less than PLAnkton for a good PLA replacement. I still sell genuine ST M27C512-90B6 for a pityful 3$US each.

What was posted on the Tynemouth Software blog is pretty much exactly what you shouldn't do.

P.S.: 450ns ... oh please!

P.P.S.: Using a PROM as a PLA can be even more energy efficient than PLAnkton. PLAnkton uses 22mA, the M27C512-90B6 from ST will work with only 10mA and finally the Atmel AT27C512R-45PU uses a pityful 4mA to do the same job. If you use a PROM as a PLA in your C64 then you can use the 1541 Ultimate 1 or 2 with an original C64 power supply - no need for a boosted PSU. (the 1541 Ultimate uses 130mA)
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: Another one thinks the earth is flat...

Post by eslapion » Sat Jul 02, 2016 6:28 am

I wanted to sum up here.

This is what I know of using (E)PROM as subsitutes for PLAs on the C64:

- At least 25% of (E)PROMs rated for 90 to 120ns response speed work properly as a PLA on the C64. The cartridge Super Zaxxon uses a flip-flop tied to ROML access and is a good way to test for (E)PROMs which work well or not as PLAs.

- The ideal CASRAM latency is 40ns.

- The last production PROM chip which works perfectly reliably as a PLA substitute with no additional components is the M27C512-90B6 from ST. It was discontinued around 2011

- All M27C512-90B6 found on eBay AliExpress and others turned out to be rebranded Winbond 27C512 and DO cause glitches

- It is possible to use Atmel AT27C512R-45PU as PLA substitutes IF and only IF you filter the very fast glitches this chip will generate. Ray Carlsen has provided a clear documentation on how to do this.

Here:
http://personalpages.tds.net/~rcarlsen/ ... rompla.txt
The Atmel series of OTP EPROMs
(one time programmable) are still available and are a good choice for a
replacement PLA but it takes some effort to make them work reliably. The
best substitute seems to be the 45nS version (70nS also works) although
all EPROM based PLA replacements need "filtering" to make them work
properly and not cause damage to the computer or peripherals. If any
EPROM is used, the output lines MUST be filtered to prevent damage to
CMOS devices such as a JiffyDOS Kernal upgrade or external carts such as
the 1541Ultimate. This filtering takes the form of series resistors of
150 ohms on six of the EPROM output data lines.
When an EPROM does the "calculations" needed as a sub PLA, it can
sometimes drive all outputs low at the same time for a fraction of a
second. Original NMOS chips in the computer may be tolerant of such
errors but newer CMOS will not be. The EPROM outputs must also have
small capacitors of 150pF to ground on the downstream side of those
resistors to provide high frequency filtering of the "spikes" or noise
pulses generated by the EPROM. That was not necessary with the original
PLA because it was a different kind of logic chip. With filtering, the
replacement PLA will work fine and is safe to use. I tested it on all my
boards from the earliest 326298 and 250407 (the most plentiful) as well
as the later 250425 and 250466. Note that those two later boards already
have an 82 ohm and 150pF components on their motherboards /CASRAM line
from the factory, so those parts are not used on the sub PLA module for
the 250425 and 250466. The EPROM IC pin 18 /CASRAM line is therefore
wired directly to the plug for those last two C64 boards only. The
/CHAROM line pin 15 is also wired direct to the plug in all sub PLA
modules as it needs no "correction".
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Re: Another one thinks the earth is flat...

Post by dudz » Sat Jul 02, 2016 11:21 am

necroing a thread to beat the dead horse? yeah, why not? :)

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Re: Another one thinks the earth is flat...

Post by eslapion » Sun Jul 03, 2016 1:04 am

dudz wrote:necroing a thread to beat the dead horse? yeah, why not? :)
See what a great positive contribution you just did to this thread.

I posted the above message to give more details and to show this is not about saying PLAnkton is better than whatever.

It's about doing it the right way if you want to use a PROM or EPROM as a PLA substitute. Contrary to what Jens Schönfeld and Groepaz have claimed, it can be done safely but if you use a modern PROM, you can't just plug it in there. There are simple steps you have to take.

Obviously, you understood all of that... right ?
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Re: Another one thinks the earth is flat...

Post by dudz » Sun Jul 03, 2016 6:03 pm

yes, i understand that you keep tooting the PLA horn and have a strong urge to express your feelings about it for some reason.

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Re: Another one thinks the earth is flat...

Post by eslapion » Sun Jul 03, 2016 6:14 pm

@dudz
As it was said in another thread, it's an unfortunate fact there's a lot of ignorance in the Commodore community

I guess when ignorance is willful then it's a bit of a lost cause...
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: Another one thinks the earth is flat...

Post by eslapion » Sun Jul 03, 2016 11:35 pm

dudz wrote:yes, i understand that you keep tooting the PLA horn and have a strong urge to express your feelings about it for some reason.
Great accomplishment... I revived this thread because I wanted to make sure if people look on search engines for ways to use a PROM based PLA they find the correct information rather than wreck their machine or end up with a solution that causes weird random problems.

Instead, what will they find now? You bitching. What a great service to the Commodore community... be proud!
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: Another one thinks the earth is flat...

Post by Borat » Mon Jul 04, 2016 11:59 pm

So what is the best solution to the PLA replacement issue at present? Is it the M27C512-90B6 or PLAnkton (and the likes)?

I just killed a PLAnkton by shorting 2 pins on the character ROM with a scope probe :( but I ordered a few replacements from Fredric - just waiting for delivery now...

I have an EPROM programmer for both my C64 and and PC - I'd like to be able to do my own in future to save on both cost and waiting time. Any pointers here would be appreciated.

Also, @eslapion I have a few JiffyDOS EPROMs installed for many years now (1571, 1581, C64 etc) - I'd like to reclaim these EPROMs and replace them with OTPs. Any suggestion as to which OTP I should use?

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