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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 12th Feb 2021, 2:39 am   #581
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Default Re: Non-working Commodore PET 3016

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Originally Posted by Mark1960 View Post
Iíve read a few times in different fora that one method of recovering data from an eprom that has started to lose its memory due to old age is to vary the supply voltage. If this is correct then reading the eprom at 3v3 might not mean it would work correctly in its original 5v system.

Also if you read an eprom and find it doesnít match the required content, how do you know if its because you read it at 3v3 instead of at 5v.

For fault finding its probably better to read devices as close to the correct spec as possible.
Well some EPROM-Programmers, like Dataman / ELNEC ones (and probably v.expensive Data-I/O etc) do "Voltage-Margining" when verifying a device (after programming etc). using Vcc +/-5% or 10% (sometimes configurable)
And I have sometimes found ones that won't read the same at one of these, compared to nominal Vcc / the opposite Vcc margin voltage.

IIRC, it is reading at the upper-voltage that is most-likely to give problems, due to internal reference-point scaling with Vcc. So setting Vcc at lower limit may give you best chance
But operation below the EPROM's min. Vcc spec. may not work (especially over temperature) and I think CMOS ones don't have a lower Vcc spec. (Unlike 74HC logic)
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Old 12th Feb 2021, 2:57 am   #582
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Default Re: Non-working Commodore PET 3016

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Originally Posted by SiriusHardware View Post
In today's news, Colin's PROMs arrived today and have now been read.

Results:
UD6 - matches "basic-2-c000.901465-01.bin", checksum = 3838
UD8 - matches "edit-2-n.901447-24.bin", checksum = FDBF *
UD9 - matches "kernal-2.901465-03.bin", checksum = 7C98

* although an 8K device this IC only contains 4K of code, the checksum is of the lower half (0000 - 07FF). Upper half contains all FF.

UD7, marked 901465-02 - is dud. Contains almost all 0x80, the first two lines contain Strings of 'BE', 'A2', 'A6' and '82'. It's not a well chip, as we had already feared from Colin's measurements on it when compared to its sister UD6.

For replacements, there are a couple of direct-fit options that I can see.

One is to use an 8K / 24 pin MCM68764 EPROM with the 4K of code programmed into the upper half. The only pinout difference between the original PROM and the MCM68764 is pin 21: On the original PROM it is an active-high chip select: On the MCM68764 it is A12, the highest address pin, which, when plugged into the socket in the PET, is held permanently high, selecting the upper half of the IC.
>>

>>

Those are my thoughts for possible substitutes - can anyone see any snags with those or suggest anything else which might be drop-in compatible?

From a recent thread, here: https://groups.io/g/DataioEPROM/message/5787 they suggested that the Chip Select / Enables are the 'standard' active-low polarity - On C64 KERNAL at least, but might have done it differently on the PET.
And you can also use the very-similar MCM68766 - Although both MCM6876x ones are now quite difficult / expensive (>=$20) to buy.

I also found some links to these handy PCB's: http://store.go4retro.com/2364-adapter/ that let's you use a standard 2764 to replace a 2364
Or with links to set CS polarity: http://store.go4retro.com/23xx-adapter/

- The blank PCB's are quite cheap, at $1.50, but no-doubt postage from USA could be quite a bit more than if there's any UK suppliers / getting them from China.

They also do one for the obscure MOS 6540 ROM's, on some PET's: http://store.go4retro.com/6540-adapter/
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Old 12th Feb 2021, 4:49 am   #583
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Default Re: Non-working Commodore PET 3016

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Originally Posted by SiriusHardware View Post
See also the post by Dave Cox, #573. I am not absolutely certain that my programmer can programme the 25P32 as there isn't a specific selection for that variant in my programmer's software. I'd have to look at what the difference between the 'P' and 'non-P' variants are. It might just mean 'plastic' rather than ceramic. If I can't do them maybe someone else here can.

It seems TI put a P in the middle, for non-eraseable PROM-Only versions (aka OneTimeProgrammable) in a Non-windowed Plastic-package: https://picclick.fr/Tms25P32Nl-Dip24...687215193.html
https://www.elnec.com/en/device/TI+(TMS)/TMS2532/

I couldn't find a datasheet that covered the TMS25P32,
but I did find one for the TMS27P32 PROM (a separate from the TMS2732 EPROM). Although later-on, they just had a single one for the TMS27(P)C32 (E)PROM.


So if your programmer supports any 2532, with then it should do the TMS25P32, if the right Vpp is used (Probably 25V, without an A etc. suffix, but could try 12.5V / 21V / 25V in order, if in doubt what the correct Vpp is for that, until it programs)

Apparently, the 'P' (OT)PROM versions were introduced a bit later, and were quite a bit cheaper without a quartz-window ceramic package. But probably rather harder to find these days, and may be difficult to trust that they haven't been already programmed so little use.
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Old 12th Feb 2021, 11:02 am   #584
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Default Re: Non-working Commodore PET 3016

fyi, I have made contact on the other forum and John is checking to see what the ICs are that he has to see if they will suit.

Colin.
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Old 12th Feb 2021, 1:10 pm   #585
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Default Re: Non-working Commodore PET 3016

OK Colin, let's hope he has something for you there.

Information for Owen: The original Mask-Programmed PROMS used in the PET have -up to- three CS pins, named CS1, CS2, CS3. The exact function and 'sense' of these pins was programmed at the manufacturing stage, and the ones in the PET are set up like this:

CS1 (Pin 20) - Active low chip select
CS3 (Pin 21) - Active high chip select

CS2 (Pin 18) - programmed as address line A11. That is why, when you look at the PET circuit diagram, the PROMs all have a CS1 and CS3 but mysteriously, no CS2.

In the PET, pin 21 (active high chip select) is held at permanent +5V which is fortunate, as that pin coincides with VPP which also needs to be held at +5V for read mode on on 2532, etc EPROMs.
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Old 12th Feb 2021, 11:57 pm   #586
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Default Re: Non-working Commodore PET 3016

[QUOTE=SiriusHardware

>>Results:
>>UD6 - matches "basic-2-c000.901465-01.bin", checksum = 3838
>>UD8 - matches "edit-2-n.901447-24.bin", checksum = FDBF *
>>UD9 - matches "kernal-2.901465-03.bin", checksum = 7C98

>>* although an 8K device this IC only contains 4K of code, the checksum is of the lower half (0000 - 07FF). Upper half contains all FF.


Information for Owen: The original Mask-Programmed PROMS used in the PET have -up to- three CS pins, named CS1, CS2, CS3. The exact function and 'sense' of these pins was programmed at the manufacturing stage, and the ones in the PET are set up like this:

CS1 (Pin 20) - Active low chip select
CS3 (Pin 21) - Active high chip select

CS2 (Pin 18) - programmed as address line A11. That is why, when you look at the PET circuit diagram, the PROMs all have a CS1 and CS3 but mysteriously, no CS2.

In the PET, pin 21 (active high chip select) is held at permanent +5V which is fortunate, as that pin coincides with VPP which also needs to be held at +5V for read mode on on 2532, etc EPROMs.[/QUOTE]

Thanks for the Info. Yes Commodore were often keen on having extra chip selects on the memories (I do recall them having 5 on one), to save a bit on external address-decoding logic.
Although if one active-high CS is permanently tied high, then that's one less that's really needed to have to emulate with an EPROM, and getting back to more like the usual 2 (or only 1 with 8K squeezed into 24pins)

I didn't think you could program as such where Address lines went. And maybe they dropped the 'CS2' to maintain naming on previous half-size devices but wanted Address-line compatibility with standards for 4KB? ones.

So with only 1 active-low CS required, then those MCM6876x ones should work with no extra logic required.


Re: UD8 being an 8KB device , with 'Upper' half reading all FF
Could it be that it was actually a 4KB device, with an active-low chip select connected to the 'A12' pin. As that may also result in FF being read if programmer has slight pull-ups on its data-lines, to prevent floating?
I do recall seeing some programmers read all FF's with no / faulty IC present.
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Old 13th Feb 2021, 11:07 am   #587
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Default Re: Non-working Commodore PET 3016

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Re: UD8 being an 8KB device , with 'Upper' half reading all FF
Could it be that it was actually a 4KB device, with an active-low chip select connected to the 'A12' pin.
I had my sums mixed up there in any case, the PROMs are 4K devices (not 8K as I said - too many late nights) but UD8 contains only 2K of code. It may well be a 2K device with an active low CS2 on pin 18, rather than A11.

The next time I'm using the programmer I will try reading 'no device' and see whether the data reads in as 00 or FF.

Fortunately UD8 is not the one we need to worry about as it was OK. Hopefully Colin will get some good news re: availability of suitable replacements from that source mentioned earlier.
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Old 13th Feb 2021, 7:04 pm   #588
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Default Re: Non-working Commodore PET 3016

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Originally Posted by SiriusHardware View Post
There is, incidentally, an active user of this forum who also goes by the same handle as the vcfed guy, 1980s_john. Not necessarily the same person, but maybe worth a PM to ask?
Yes I'm the same guy! I grabbed the handle to match my website:

https://vintagecomputers.sdfeu.org/hp85/index.htm

Regards,
John
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Old 13th Feb 2021, 11:23 pm   #589
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Default Re: Non-working Commodore PET 3016

Some alcohol and a razor blade reveals neither 25P32's I offered have windows!

Seemingly, a bonded ceramic lid where the window would normally be, with a carefully stuck on label.
I've seen plenty of the plastic package PROM's but none like these. It looks like they haves used an identical package but bonded a lid over the hole. Duh

Now, where's my Widlariser ...

dc
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Old 13th Feb 2021, 11:52 pm   #590
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Default Re: Non-working Commodore PET 3016

Thanks for looking Dave, I'm afraid if they have labels on that makes them more or less 100% likely to be programmed already.

It sounds as though Colin already has a dialogue going with 1980s_john (hello by the way John, thanks for confirming it is you here as well as there). So let's see if anything comes of that.
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Old 14th Feb 2021, 12:21 pm   #591
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Default Re: Non-working Commodore PET 3016

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Originally Posted by 1980s_john View Post
Yes I'm the same guy! I grabbed the handle to match my website:

https://vintagecomputers.sdfeu.org/hp85/index.htm

Regards,
John
Nice website by the way ex MK14 owner... and one of the few places to have anything on the PowerTran PSI80. Totally Off Topic sorry but, you don't happen to have a copy of the TRAP assembler for the Transam do you?
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Old 14th Feb 2021, 12:36 pm   #592
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Default Re: Non-working Commodore PET 3016

I'm in touch with John with a couple of back and forth emails so that hopefully will result in a nice new UD7 soon.

is there anything I can safely check with regards to the monitor electronics while I'm waiting?

Colin.

Quote:
Originally Posted by SiriusHardware View Post
Thanks for looking Dave, I'm afraid if they have labels on that makes them more or less 100% likely to be programmed already.

It sounds as though Colin already has a dialogue going with 1980s_john (hello by the way John, thanks for confirming it is you here as well as there). So let's see if anything comes of that.
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Old 14th Feb 2021, 12:56 pm   #593
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Default Re: Non-working Commodore PET 3016

Not really, because the best / most convenient source of test signals for the monitor is the mainboard. If we get to the point where your scope shows video and sync signals coming out of the mainboard but still nothing on the monitor, that's the time to go looking at the monitor.

Wait until you have a replacement UD7 - who knows, that may be all the machine now needs to make it work. (He says, optimistically). .

Best not to over-think things at this stage - whenever you find a definite fault (as you have with UD7, which is a big step forward), fix that first and see what effect that has before moving on to look for any further faults.
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Old 14th Feb 2021, 1:07 pm   #594
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Default Re: Non-working Commodore PET 3016

I admire your optimism...

Colin.

Quote:
Originally Posted by SiriusHardware View Post
Not really, because the best / most convenient source of test signals for the monitor is the mainboard. If we get to the point where your scope shows video and sync signals coming out of the mainboard but still nothing on the monitor, that's the time to go looking at the monitor.

Wait until you have a replacement UD7 - who knows, that may be all the machine now needs to make it work. (He says, optimistically). .

Best not to over-think things at this stage - whenever you find a definite fault (as you have with UD7, which is a big step forward), fix that first and see what effect that has before moving on to look for any further faults.
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Old 18th Feb 2021, 12:32 pm   #595
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Default Re: Non-working Commodore PET 3016

Ok - it's here (thanks John). Are there any tests I should perform before I pop everything back in and power on?

Colin.
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Old 18th Feb 2021, 12:54 pm   #596
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No, just put everything back how it should be (all CPU pins fitted) and just see what happens now. If it miraculously works, it will take the screen a few seconds to light up.
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Old 18th Feb 2021, 3:04 pm   #597
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Default Re: Non-working Commodore PET 3016

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No, just put everything back how it should be (all CPU pins fitted) and just see what happens now. If it miraculously works, it will take the screen a few seconds to light up.
Sadly, no miracles. Not a sausage.

Colin.
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Old 18th Feb 2021, 3:18 pm   #598
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Default Re: Non-working Commodore PET 3016

OK. With the new UD7 in place and everything else as it should be, do you get continuous activity on A0? (6502 pin 9).
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Old 18th Feb 2021, 4:36 pm   #599
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Default Re: Non-working Commodore PET 3016

Nope. With all ROMs inserted, the only way I get a clean pin 9 reading on my scope is with pins 30, 31 and 32 removed from the 6502 socket.

Colin.

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OK. With the new UD7 in place and everything else as it should be, do you get continuous activity on A0? (6502 pin 9).
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Old 18th Feb 2021, 7:12 pm   #600
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Default Re: Non-working Commodore PET 3016

I must admit I've got a bit lost with this in view of the thread length and the number of tangents. It might be worthwhile at this point summarising which components have been changed and which are known to work or otherwise. Just a thought.

Alan
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