Old MOS Mask-Programmed ROM forgetfulness?

Pete Lancashire pete at petelancashire.com
Wed Feb 17 21:05:13 CST 2016

I was about ready to recommend the same approach. Speed is not the issue.
Then when if the time ever comes to replace the part one could if have to
build a board to do any level/timing shifts.

A solution I've used before.

On Wed, Feb 17, 2016 at 5:52 PM, Rick Bensene <rickb at bensene.com> wrote:

> Brent Hilpert wrote:
> > Apparently there actually is an equivalent EPROM, according to this
> > datasheet for the MM4203/MM5203 EPROM:
> >       http://www.datasheetarchive.com/dl/Scans-006/Scans-
> > 00137265.pdf
> >
> > It states they are pin-compatible to the MM5213/MM5231 mask ROMs.
> > The EPROM even has the selectable configuration mentioned by Rick.
> > (This is the only mention I've found of the 5231, I haven't come
> across this
> > Nat Semi ROM series before.)
> A great find!  Sadly, though, I can't find that even the Data I/O 29B
> Unipak supports programming this device.
> My other ROM programmers don't support the MM5203, either.  I suspect
> that this was a fairly obscure device.
> >
> > Similar pinout to the 1702 (quite different than the industry standard
> of the
> > 2708,2716,2732,etc.)
> Yes, but there are enough differences that building an adapter, and
> getting it to work is probably not worth the effort.
> >
> > I expect they're too early and too uncommon to be covered by anything
> > other than a specifically-targeted programmer from the period.
> I suspect that National probably offered some kind of programmer for
> these devices, but, as Brent said, it was probably very targeted to the
> specific device family.  Finding something like this today is probably
> like finding Hen's Teeth.
> > It shouldn't be difficult to read them either way - adapter for an
> > reader or microcontroller, with additional power supplies as
> necessary,
> > might have to consider power-sequencing issues though.
> I think that this is the approach that I'm going to have to take.  I
> have a little microprocessor development system that has a bunch of
> programmable TTL I/Os (probably need some pullups on the outputs to
> drive the address lines), and perhaps some kind of switching on the -12V
> supply to keep the power levels appropriate, and write a little code to
> cycle through the address lines and grab the data, and spit it out in
> serial form to a PC.
> >
> > Rick, what calculator are they in?, I'd be interested in looking it up
> on your
> > site.
> I don't have it documented on the Old Calculator Museum site yet,
> because I generally only put calculators up on the online exhibits page
> that are fully operational.  I've got a slew of machines that aren't on
> the website because they require repair.  Sadly, repair on these old
> machines can chew up a huge amount of time, so it's slow going.  Maybe I
> have to change my policy on this, but it's a tough call.
> The calculator in question is a Singer/Friden 1155A.
> It is a desktop printing scientific programmable calculator.   It is
> quite sophisticated, but, by the time it came to market (mid-1972),
> Singer had pretty much decided that the calculator biz was a bust, and
> has pretty much killed off what was left of Friden's calculator
> development team.  Along with that, Hewlett Packard, Computer Design
> Corp., and Wang pretty much owned the high-end calculator market, making
> it tough for anyone else to compete.
> The machine is rather uncommon, because of the factors about, and also
> because simply didn't sell very well, mostly due to a lack of desire or
> understanding on the part of Singer's salesforce to figure out what
> markets to sell it into.
> The introduced machine used a modified version of the serial printer
> used in earlier 115x-series calculators.
> It uses three TI(TMS3414LC)  or Signetics equivalent 1K-bit MOS shift
> registers for program storage, and four  Intel 1101A MOS SRAM chips for
> microcode internal working registers and memory register storage.    The
> machine has 20 memory registers accessible to the  user.
> A later version of the 1155, called the 1155A, switched from four
> 1101A's to eight 2102 SRAM chips, and upped the memory register capacity
> to 100 registers.  Of course, some firmware changes were made to
> accommodate the additional RAM.
> The machine uses SSI and MSI DTL and TTL logic for the ALU, Data
> Routing, and the timing and control logic.
> I do have microcode ROM listings for the 1555, but since the machine I
> have is the 1155A, there are likely to be some changes, both in terms of
> fixes from the original firmware, as well as the modifications needed to
> make it work with the additional RAM.     So, if a ROM that contains
> changes from the original code is bad...well, it's not terribly likely
> that I'll be able to fix it unless I can reverse-engineer the microcode.
> Yet more time that I probably won't ever have.
> -Rick Bensene

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