Hello,
it seems alreday clear that the only way to upload waypoints or routes
to a GNS340/530 is to simulate a similar unit on a PC and use the
cressfeed function.

It also seems qite clear from the installtion handbook that crossfeed
is through one of the RS232 ports, good thing.

Does anybody, in the meantime, found some specifications about the
protocol used? I could write the software, but I need something to start
from.