Jim Macklin wrote:
I was looking and found this Garmin page
http://www.garmin.com/support/commProtocol.html
It seems to be the start of the answer to the question
previously asked about transferring waypoints.

As far as I know, that is the protocol for handhelds, and I successfully
usd it since it was undocumented. For the panel mount units, this
protocol is unusable and the correct one seems undocumented.