Old MOS Mask-Programmed ROM forgetfulness?

[Brent Hilpert]

On 2016-Feb-15, at 11:25 PM, Eric Smith wrote:
> On Mon, Feb 15, 2016 at 11:31 PM, John Robertson <jrr at flippers.com> wrote:
>> 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.
> 
> They're not PROMs, they are masked ROMs, and there is *NO* equivalent
> PROM, so it's unlikely that there's any support for reading them on
> any PROM programmer.

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.)

Similar pinout to the 1702 (quite different than the industry standard of the 2708,2716,2732,etc.)

I expect they're too early and too uncommon to be covered by anything other than a specifically-targeted programmer from the period.
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.

Rick, what calculator are they in?, I'd be interested in looking it up on your site.