The serial ports of the RFX9600 only use pins 2, 3 and 5 and are functionally the same as a PC com port. So pin 3 is data from the extender to the device and pin 2 is data to the extender from the device.

Manufacturers often use the terms TX and RX but these can be confusing without knowing if the device is DTE or DCE, as TX may mean an input that has to be connected to a TX output. (Recall that when connecting DTE to DCE a pin-to-pin cable is used so a signal wire has the one name but at both ends, even though one end is an input and the other an ouput)

A quick way of determining if a pin is an input or an output is to use a voltmeter. Measure the voltage between pin 2 (or 3) and pin 5. If the voltage is somewhere in the range -3V to -12V then it is an output. If it is about 0V then it is an input.

When testing RS232 connections, it is often worth swapping over pins 2 & 3 at one end, however some devices lock up if connected the wrong way round and even when the connections are swapped to be correct will still not work. So a good tip is to switch off the extender and the device during any rewiring.