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Hello,

Starting a new thread, although this is a direct continuation of an earlier one.
/g/HP-Agilent-Keysight-equipment/message/135714

I have verified both reading from, and writing to the A13 Xicor x28256 EEPROMs using a single Arduino Mega2560 and _many_ DuPont wires.

I do run into a problem however. It seems like not all ICs are written correctly. Out of 18 ICs written to, some 12-14 are completely verified OK, but then a few don't verify correctly for all byte positions.
The Xicor datasheet (appended) describes both a software based write protection mechanism, how to deactivate this and how to write up to 64 contiguous bytes (page write).

From what I can see using a logic analyzer,? it is clear that write protect is deactivated and bytes are written with less than 100 us separation and at least 10 ms internal write time between pages. Still, the data isn't verified properly.

Has anyone else run into problems writing to these chips or has any experience with working with them?

Regards,
? Staffan

Hi.

As in all things EEPROM related to programming trouble.

'Sope the Power rails, make sure they are not sagging during the actual writing phase, even for a fraction of the time..? Also, the actual address and data line signal voltages need to be "up to snuff" relative to the EEPROM's data sheet (probably needing decent buffers) along with the timing values too.

Commercial programmers have *Very* strict regulation during programming, and then verify them at the minimum, nominal and maximum specified Vdd rail voltages to ensure things are all good.

Modern EEPROMS are not as easy or forgiving as the old-school 27x series EPROMS to use.? (From first hand experience!)? They are easier to damage due to ESD though!? (Also, First hand experience!)

Take care.

Dave B.

--
Sent from a MicroSoft free zone:

Hello,

Good points. I checked voltage and noticed only approx 20 mV drop during access to the ICs. Only checked one of the ones that were successful in writing. Will check the other ones also. Away from my lab right now so it will take a few days though.
Being an HP design of the 1980-ies, I would expect those issues to be taken care of, but perhaps a failing cap?

All signal lines to the EEPROMS are buffered on the board by the way and the Arduino seems to output levels well within TTL requirements.

I'm thinking if there is something with the IC itself, but wonder if there is really anything that can degrade from age? It is not that the complete IC is dead, but rather just bytes are off.

I know people have updated the firmware, but not sure if this was an immediate success or if this kind of behaviour is common - hoping there may be a workaround...

Regards,
? Staffan?

If you wind up needing help, I can write a good Eprom for you

Cheers!

Bruce

Hi Bruce,?

Thanks for the offer! Much appreciated, but what I really would like is to make sure I write to the EEPROMs?correctly. Is your impression that all writes work immediately or do you have to do repeated writes in order for the FW to be correctly entered?

I believe you have some of Wayne's documentation, and possibly also the code he used for writing to the x28256 EEPROMs? It would be great if you could upload this here to have a look at.?

I think I'm fairly close to having working code - only a few ICs won't accept data properly. Possibly the code is OK and I only have some bad ICs.

My goal is to make sure I have a working solution and I can then upload this code for anyone to use. It would then be possible to read/write the A13 EEPROMS using an Arduino MEGA2560 and DuPont cables only.?

Regards,
? Staffan

First off, are talking about the EPROM on the CPU board or are we talking about the EEROMs on the program memory board.?

I have had some problems with the EEPROMs using Wayne's (ZL2BKC) reader/writer.? ?I have several EEPROM boards and have rewritten them all - one seems to work after writing, but fails some time later (days) - my conclusion is that one of the EEPROMs have a problem.? I have written the particular board multiple times with the same result (erased and rewritten).? What I have not done is to try to overwrite the EEPROM without erasing it.? Not sure of Wayne's code will do that, but I will eventually get back to the project and try to see if I can do that.

Cheers!

Bruce

This is the EEPROMs on A13 board.
It's a bit discomforting if you don't get writing to the Xicor x28256 to work properly. What I'm a bit curious of is how Wayne's code does the writing.

In my current code, I simply write a page and then wait for 10 ms to make sure the ICs are ready for next page. Perhaps a better way would be to inquire the ICs status signals (b7 and b6), thinking that internal write procedure may take longer than specified due to age.

If you have the code of Wayne's reader/writer, it would be good to have a look. Perhaps there are comments there that can tell some about his findings. As I understand, he must have been able to at least write one complete board since he managed to crack the FW key check.

Regards,
? Staffan
?

I have successfully written at least 6 boards - only one has the failure described.? I'm (reasonably) sure it is weak EEPROM.

It will take me a bit to dig up my verson of Wayne's code, but I will re-post it for you

Hello,

I have successfully written at least 6 boards

That was very good to hear!?

?I'm (reasonably) sure it is weak EEPROM.

I will set up a diagnostic test for the board to see if I can spot which ICs are bad and which ones are OK.

Looking forward to see the code!

Regards,
? Staffan

Short update.
Two ICs were bad. Replacing these two, the A13 board passed a simple integrity test of writing 0xAA and 0x55 to each position.
Next step is to create a bin file from Wayne's 5.14 zip file, that covers the complete memory space.

On a side note. TL866 claims to write Xicor x28256, but doesn't seem to disable write protect in the correct way. Scavenged chips could not be written there, but seem to work on the A13 board.

Regards,
? Staffan