Multiplex RC SystemΒΆ
For a MULTIPLEX SRXL receiver, connect the SPKT/DSM port of the Pixhawk to the B/D port of the MULTIPLEX SRXL receiver, without using the +3,3V voltage supplied at the SPKT/DSM port of the Pixhawk and power the MULTIPLEX SRXL receiver separately. Note that you may also connect to the RCin pin or any appropriately configured serial port, See Typical Autopilot Wiring Connections
Details how to enable the SRXL signal on MULTIPLEX receivers can be found in: