It is a good question because the serial ports just give you a lovely option to select something from the drop-down menu, instead of asking you to configure the input/output with a particular protocol.
Having said that, the Trig transponder certainly mentions RS232, as does the GPS output from the Dynon. The Dynon manual also goes to great lengths to tell you what information is contained in an NMEA sentence (which happens to include all the data you would expect to flow between the units you've mentioned). I certainly have NMEA (Full) selected for GPS output from my HDX to PilotAware and all the units you're talking about are serial connections. Given they are RS232 (serial) AND Dynon talk so much about NMEA, I can only imagine that would be the answer and it's certainly what I would tell them.
As usual, it sounds like the LAA is trying to re-invent the wheel, instead of just letting the manufacturers who know about these things do their job. I can just imagine someone at the LAA trying to tell Dynon or Garmin that they don't like their choice of protocol. There is no reason at all for the LAA to know whether it's NMEA, GDL90 etc etc. That's why Dynon make it so plug 'n' play and why the BMAA is SO much better
Yeah, I know that last bit doesn't help you at all. I'd tell them NMEA and get them to prove anything different. If they do, then ask them why they asked in the first place if they already knew the answer
