21MX proms (per request)

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 repair. 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