The Start Character, when read on the Serial Line, can be used to initiate a new connection for a Tunnel in Connect Mode and enable a Tunnel in Accept Mode to start listening for connections.

The Stop Character, when read on the Serial Line, can be used to disconnect an active Tunnel connection.

Optionally, the Start/Stop Characters can be echoed (sent) or not echoed (not set) on the Tunnel when read on the Serial Line.