The TSIP protocol is the same one we all know and love. But some of the values in the commands are different, particularly the set_io_options command that sets which commands that the receiver sends automatically and in what format it sends them. I suspect that, alone, would make dropping in a Resolution-T not work (the pinouts are compatible as long as the Datum does not use the secondary serial port, you add a 3V regulator, and do something with the antenna power pin.. on the SV6 that is the second serial port TXD line... the second serial port is for DGPS corrections). There are also a few other commands that the SV6 supports and that the Res-T does not. I don't know if the Datum uses those. Plus the newer Res-T's (like the SMT360) use a different command to send the satellite signal/position data. ---------------- > Do you know if the protocol is real-close or just similar enough to use the same name?