The ones you have to watch out for as a rule are those made by Mostek. Not sure of the date when they changed to recipe.
If your still in/near PDX I will be getting my Unisite+ back in March and I may have a working Model 29 that you can borrow. -pete On Mon, Feb 15, 2016 at 10:25 AM, Rick Bensene <ri...@bensene.com> 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 > > > > >
