1. Connect P1 and P3 together.
2. Switch the receiver on.
3. Remove the connection.
The led on the receiver will come on solid and flicker:
* once a second if Selecta is disabled.
* twice in 1.5s if Selecta is enabled.
* three times in 2s if Selecta is enabled with Tx_Change.
The setting will increment or wrap each time the procedure is repeated.