Is the D-STAR module installed?
Yes it is
Are you tuned to a D-STAR channel at the time you're attempting to program it?
Yes I am.
Do you have GPS turned on? If so, I think you'll want all of that disabled. Ideally, disable the GPS stuff and tune both sides to FM channels before trying.
Alternately, use an OPC-478 style cable and eliminate all the above potential for conflict. They're cheap on eBay :)
But what I have just found is this page:
http://www.dj0abr.de/english/technik/aprs/aprs_mit_dem_ic.htm
And if you scroll to the middle you will read that 2820 needs -8V to input pin, but my usb-to-serial adapter, outputs only -6,2V.
Maybe this is the problem!!!
Doubtful. Most USB-to-serial adapters don't generate proper RS232 anyway, and many are only really getting +/-5V on those lines. I've never had one that the 2820 seemed to balk at. That said, who knows.
--Dan