Sorry if I'm a bit late to the party, but I've been following the TIL311 replacement
thread and felt it and the rarity of 74C922's makes the Quest/Netronics Elf keyboard
more difficult than needed today. I checked out the RCA Microterminal as an alternative.
This was used with one of the Evaluation Kits. It is described in MPM- 212. Although
RCA's design uses their old CDP1652 port chips, these could be replaced with modern
tri-state buffers and latches. There is no hex->7seg decoder as this is done in the
accompanying UT5 monitor. UT5's functionality is much like other monitors of the day.
MPM-212 contains an assembly listing of UT5. It's 512 bytes, 8000-81FF, and needs 32
bytes at 8C00 for a scratchpad. While the need for a ROM is a bit of a pain, it's not
as bad for the DIY'er as this would have been back in the day. I suggest that due to
the better availability of parts, the functionality of UT5, and the hex keypad as the
authentic retro experience, this is a good solution for a new Elf build. Interestingly
Mike McLaren, in a recent post in this thread, suggests a similar scheme which uses
a PIC microcontroller for the multiplexing.