I finally found how to proceed :
11 Millisecond frame rate : for digital servos ( Green light on RX1202 )
22 Millisecond frame rate : for analog servos ( Red light on RX1202 )
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After binding completed and RX powered on :
Press & hold the switch for approx 5s / 6s
Both indicators will turn on.
Release the switch & press it again :
The frame rate can be changed alternatively : the LED will turn red or green only depending on frame mode selected.