Old MOS Mask-Programmed ROM forgetfulness?

[Eric Smith]

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.

> Part of the
> problem with the early PROMs is they needed a Sync or Clock signal to be
> able to be read.

The MM4221/5221 is fully static, so it doesn't have that particular problem.

It's PMOS, and needs +5V and -12V supplies. The outputs are
TTL-compatible, but the inputs technically are not, due to Vih min of
3.0V. Could be driven by TTL with a pullup resistor, or by CMOS.