Old MOS Mask-Programmed ROM forgetfulness?

dwight dkelvey at hotmail.com
Tue Feb 16 14:43:17 CST 2016

It is interesting, I have 1702As that were programmed in 1973 sometime
and they still have their data ( used on my SIM4-01 ).
And yes, I have them backed up.
It is interesting that Data I/O has added supply current
checks. I've used many home made pin adapters over the
years to read old ROMs, as John probably knows, as some
were from pin ball machines.
Some of the earlier ROM also had address latches built in,
making reading tough.
Anyway, making pin adapters is not that hard. I usually stack
a three solder pin, machine pin sockets.
In place I don't want any connection, like Vpp, I pop the pin
out. In other places where I need to rewire, I break the
solder pin off and file it down a little so it won't short.
I do connections and sometimes vector side boards with
soldered wire wrap wire. Often I need switches or sometimes
logic off to the side.
It only takes 15 or so minute to put a typical adapter

From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Brent Hilpert <hilpert at cs.ubc.ca>
Sent: Tuesday, February 16, 2016 11:06 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Old MOS Mask-Programmed ROM forgetfulness?

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:

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.

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