ROM Emulator for Vintage HP Series 80 Computers

ROM emulators have become extremely common for classic consoles like the NES and Game Boy, but what about earlier computers that also used edge-connector-style expansions?


HP Series 80 group member Tim Nye developed a Teensy 3.6-based ROM-emulating plug-in module that allows users of the early 1980s pre-PC HP 83/85 and 86/87 to select any of the systems’ available ROMs to be loaded from flash memory.

The board includes some unique features, such as a 6V level shifter to bridge the HP’s bus with the Teensy’s 3.3V logic, and a diode to prevent the HP’s 5V power from flowing via USB to a connected computer during programming. One interesting challenge was that the Teensy needs to boot before the HP, but the /HALT line on the HP’s bus can be driven by the Teensy to only permit the CPU to start once it’s ready.

The board appears to be a one-off with no information on purchasing or creating one’s own, but the HP Series 80 group is an active community, so drop them a note if you have a Series 80 with an empty expansion slot!