The remaining microcontroller ports can be found on the back side of the module. From left to right are ports labeled Serial, Rx2, and Rx1.
The serial port is for interfacing with the programming module.
Ports Rx1 and Rx2 are for the radio receivers. Rx1 is the primary port to which the receiver module is connected to. A second receiver, if used, would be plugged into Rx2.
Next to the Rx2 port is the battery port which connects to the 7.2V source, either the battery container holding 6AA batteries or the rechargable battery from the optional power pack.
Finally, on the far right is the power switch for the module.