All that is of course somehow good, but not exactly what is needed for PIC Nixie clock. It's like someone was asking about how to use transistor, but he'd being taught first what is Epitaxy, Czochralski method or Gallium nitride doping. We don't need that.

All what we need for clock is something like this:

1. flash this firmware.hex into ESP
2. Connect it's pin #4 (or whatever), to your PIC port X
3. Use SERIN X,Y,Z statement to get the current time


That's all.