The GV & GT are Binary-only units.
The GV6 & GT6 units with serial numbers of 02061700000 and higher have both Binary and ASCII capability.
To change from Binary to ASCII, type the command ASCII1. To change from ASCII to Binary, type ASCII0.
The GV6K & GT6K have the same controller board that is used in the 6K and therefore have ASCII only. The "Keep Alive" in these units is not optional. This 24VDC is required for logic power and therefore to communicate.