Looking at a machine on one of the dead branches of personal computer evolution. To make it work, I have to break out both the lathe and the soldering iron.

Make your own ROM cart:
https://alnwlsn.com/z/hpseries80/rom1...

Links:
https://en.wikipedia.org/wiki/IBM_510...
https://wolfgangrobel.de/museum/82929...
https://www.fliptronics.com/EBTKS/EBT...
https://groups.io/g/hpseries80/wiki/1893
https://www.hp9845.net/9845/tutorials...
https://www.curiousmarc.com/computing...
https://vintagecomputers.sdfeu.org/hp...