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 <ri...@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 > EPROM > > 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 > >