21MX proms (per request)

Jay West jwest at classiccmp.org
Sun Sep 6 13:41:09 CDT 2015

Several people asked, here's the scoop:

The common proms for HP 21MX M/E/F are 1K, 4K, and 8K.

1K are used for either loader roms on the cpu board or microcode on the FAB
4K are used for microcode on the FAB or FEM
8K are used for microcode on the FEM

The manuals you'll want to print and keep handy:
HP 12992 Loader Roms Installation Manual, 12992-90001 (April '86)
HP 1000 M/E/F-series Firmware Installation and Reference Manual, 12791-90001
(September, '83)
I believe these are both on bitsavers. They are "must have" manuals.

These are all bipolar proms, and most modern prom programmers will not be
able to program them. I use a Data I/O 29B (with Unipak 2B), and it can
program all these parts. Those programmers appear on ebay from time to time
at around roughly $400.

The blank proms are not terribly easy to find these days. Ebay has them
occasionally, but your best bet is sites that cater to arcade machine

Here's a non-exhaustive but useful list of compatible parts for each:

1K parts
MMI 6301
Harris 7611
Signetics N82S129
National 74S287
TI 24S10
AMD 27S21
Fujitsu 7114 (possibly 7052 as well, need to verify that)

4K parts
Signetics N82S141
Harris 7641
MMI 6341

8K parts
Signetics N82S181
Harris 7681
MMI 6381

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