"Glen Wiley Wilson" wrote in message
...
Larry's deductions are correct. In NMEA mode, your Garmin is deaf. In
RTCM
it can hear differential GPS beacon data. In GRMN mode, it can upload and
download waypoints, routes, etc, but it can't communicate with normal NMEA
equipment.

But on the garmin faqs page it says it can be done, and I remember using
this with a yeoman plotter

http://www.garmin.com/support/faqs/faq.jsp?faq=27

The autopilot can be driven from either the GPS or the plotter; whichever
one
has the waypoint is the one that generates the steering commands.

But if I cannot upload waypoints to the gps, then I would be better getting
the plotter to drive the autopilot, with perhaps a changeover switch in case
the plotter failed.



Glen Wilson
See my NMEA Instrument Repeater software
at http://www.worldwidewiley.com/3NMEA.shtml

Looks pretty neat ... are you going to release this as shareware, open
source or what ??


garry