On 02/15/2016 10:25 AM, Rick Bensene wrote:
Hi, all,
I have a question about old Mask-Programmed ROMs
The part in question is the National Semiconductor MM5231. This part is
a 2K-bit PMOS Mask-Programmed ROM, generally organized as 256x8, but
also can be organized (via a MODE pin)as 512x4 bits. In this particular
application, the parts are used as 256x8.
I'm wondering if anyone knows if these particular ROMs (from the '72
timeframe) have a tendency for bit rot over the years?
I know some of the early MOS ROMs had issues with metallization creep
that would cause data loss/corruption.
I have an old calculator that uses these ROMs as the micro and macrocode
stores.
The machine is catatonic, though the power supplies, master clock
oscillator and divider circuitry, and the other obvious stuff are OK.
I suspect it is probably stuck in some kind of microcode loop, just
cycling around doing nothing. I have not yet put logic analyzer on the
microcode latches yet, but that's probably my next experiment.
Sadly, if one or more of these ROMs (there are 18 of them!) has failed,
it likely means that the machine can't be restored to operation, as this
is quite a rare machine, and there just aren't many of them left around.
I have three different EPROM programmers, but sadly, none of them have
the capability to read these parts. I was I had a Data I/O programmer,
but alas, haven't come across one with all the Unipak modules I'd need
at a price I can afford.
Thanks,
-Rick
---
Rick Bensene
The Old Calculator Museum
http://oldcalculatormuseum.com
Rick, if you want to archive these PROMs (highly recommended) you should
be able to find a Data I/O 29B and get one of the programming packs that
supports NS chips. I may have such a combination in my collection, but
that PROM is not listed in my DATA I/O library of readable parts. Part
of the problem with the early PROMs is they needed a Sync or Clock
signal to be able to be read.
If I think of it tomorrow I will go through my sets, but the best place
right now is for you to post this request on the Data I/O mail list on
Yahoo...."Data_IO_EPROM" and see if someone there can give you better
advice.
John :-#)#
--
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Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
www.flippers.com
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