HP82143 Processor details

[brouhaha]

The processor in the printer is a mask-programmed MK3870 microcontroller (Fairchild F8 architecture) with 2KiB of ROM and 64 bytes of RAM.

I don't think you actually need to know anything about the 3870, which is good because AFAIK no one has dumped the internal masked ROM yet, and we don't have any internal HP doc such as an ERS for that firmware. The NPIC documentation that we do have gives almost everything you need to know to interface to it. At one point I had a logic analyzer hooked up to it to confirm some details, whcih I've since forgotten, but there wasn't anything unexpected.

EDITED 2023-09-20: I mistakenly originally wrote that the MK3870 had 1KiB of ROM. Also corrected a typo of 3470.