HP-42S "reinterpretation"

[BarryMead]

I have never owned a genuine HP-42s, so I would jump at the chance to buy a replica! If you can fit it all into the available ROM/RAM, it has a lot of potential. If the replica starts to sell well, there would be community based 3D printed case designs popping up to support your effort. I like your simple easy-to-solder through-hole parts design, and join with you in your belief that an HP-42s clone has the potential to re-invigorate the creative activity within the Open Source Calculator Community!

I did have one question after looking at your preliminary circuit diagram. What are the vertical rows of the keyboard matrix connected to? The charlieplexed keyboard scanners, that I am familiar with, use diodes to eliminate multi-key ghosting, or reduce the number of CPU I/O's required.