In reply to:

---

You could even place a jumper switch on the board to allow you to "route" the TTL level GPS data to the VFD allowing you to display the GPS data (assuming its in NMEA format) on your VFD as a form of system "self test".
[I think the VFD will accept regular ASCII data and show it as it has onboard Character Generator logic].

---

It can - it has a limited set of the full ASCII character set -
erm, wait. My bad. Default power-on has the full set, starting with the hex 20, the space. Everything BEFORE that is custom programming commands and such.. :>

Me.