"Glen Wiley Wilson" wrote in message
...

I forgot to mention that NMEA listeners are supposed to be isolated,
so it should be perfectly fine to attach an RS-232 talker to an NMEA
listener.

That is correct.

I'm just not sure everyone implemented that particular
feature, given the workmanship I've seen in the instruments I've
cracked open. So, for the record, when speaking for public
consumption, I prefer to play it safe.

And that is correct too. Many mfg's have just a single ended input aka 'in'
vs. 'gnd'. Even many with a + and - (differential) you cannot be sure if
they have isolation. Pity that the NMEA organisation does not 'approve'
designs. But rest asu my muxes all have optocouplers inside :-)

Meindert