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falter
March 9th, 2014, 02:01 PM
So I've changed all the chips a few times now on this Unitron keyboard and I think I'm down to the EPROM chip that serves as the controller. It's a Fujitsu D2732D. I don't have access to any dumps of the ROM.. so my question is, if I buy one of these universal programmers.. do those *read* EPROMs and dump from them, or do they only write? I'm not clear on how a 'dumper' would read from a potentially dead 2732 or if it can...

Chuck(G)
March 9th, 2014, 02:29 PM
Are you certain that the EPROM's a Fujitsu? Most Fujitsu chips start with MB..., so a 2732 would be MBM2732A.

No matter--almost any EPROM programmer that can handle legacy ERPOMs can read a 2732. However, you can get into an awful mess when trying to handle smaller devices because they tended not to be quite as "universal" in their power supply, programming and even signal conventions. So tread carefully if you run across a 2716 or 2708.

modem7
March 9th, 2014, 03:21 PM
It's a Fujitsu D2732D.

Are you certain that the EPROM's a Fujitsu? Most Fujitsu chips start with MB..., so a 2732 would be MBM2732A.
Perhaps a uPD2732D, an NEC device. NEC tends not to print the "uP" prefix (missing prefix example [here (http://www.minuszerodegrees.net/memory/chip_nec_UPD4164C-15.jpg)]).


I'm not clear on how a 'dumper' would read from a potentially dead 2732 or if it can...
It depends on the type of failure.

In my experience, when ROMs fail, the symptom is mostly that the ROM content has become corrupted. The ROM reader will read the content and present it to you on-screen. The problem becomes, are the bytes seen good or bad?
For example, if the first five bytes read are 6B 43 A2 06 77, how do you know that 6B 43 A2 06 77 is what is meant to be for the first five bytes? Unless it is written down somewhere, or a known good ROM can be used as a comparison, then you don't.

falter
March 9th, 2014, 09:51 PM
Sorry yes it's an NEC. I had it confused with another one I have.

Yeah I've been searching the web but no dice on a ROM dump of it. I'll have to keep hoping I stumble across one. How sensitive are these chips? It was weird.. I was using the keyboard to test a Rev 04 board. At one point it stopped working (only ctrl-reset) worked.. then I swapped it over to the Unitron computer.. worked again, worked again on the Rev 04 and then quit completely. Nothing risky or hazardous, or anything silly like putting the cable on backwards.

MikeS
March 9th, 2014, 10:10 PM
If you're up to it, a simple adapter that swaps a couple of pins would let you read it in one of your (working ;-) ) PETs...

Chuck(G)
March 9th, 2014, 11:11 PM
A dump of the ROM (assuming that you're able to make a decision based on the contents) will tell you if it's the EPROM or the supporting circuitry. If you don't know how to make sense of the contents, then there's no real information to be gained, is there?

Dwight Elvey
March 10th, 2014, 06:06 AM
I don't recall which way eproms go but
if it is bit rot and it is still close to working,
one could try cooling it with some ice in
a plastic baggie.
If it read out different than at room temperature,
you might be able to save the information.
As Chuck says, unless you know what to expect in
the code, you'll not get much unless there is a stuck
bit. If so, you'll know that the EPROM is bad.
Dwight

SiriusHardware
March 10th, 2014, 12:17 PM
A dump of the ROM (assuming that you're able to make a decision based on the contents) will tell you if it's the EPROM or the supporting circuitry. If you don't know how to make sense of the contents, then there's no real information to be gained, is there?

For the OP: This is a very long shot, but what's on the label of the eprom?

Is there by any chance a 4-digit hex number written or printed there?

If there is, it's a good chance it is the checksum of the data in the eprom. If you use an eprom reader / programmer (they can all do both things) to read the entire content of the eprom into your PC, or the programmer's own memory if it is a standalone one, then you can ask it to tell you the checksum of the data which has been loaded. If you see the same 4-digit checksum as is written on the eprom label, there's an excellent chance the data is OK.

If it is, you should save a copy of the code and keep it somewhere safe, and, if you are sure the code is correct, reprogram the eprom with it to reset the 'data decay' right back to zero. The data should then be good for another 30-40 years or so. As you would be writing the exact same code back to the eprom, you don't even need to erase it before you reprogramme it - just answer 'yes' when the programmer says something like 'device is not blank - do you wish to patch?' - all you're basically doing is refreshing the programming in the device, not changing it.

I would say this is good general advice for any retro computer kit which contains eprom data approaching or exceeding 30+ years old. Even if it's still working for the moment, back up the eproms and refresh them as well if you feel confident enough to do that.