Is there Port Protection on the Prolinx serial ports?

Yes, the following information outlines the protection on the Prolinx 

The Serial Port Protection

RS485/422 port interface lines TVS diode protected at +/- 26.7V breakdown voltage and +/- 24V stand-off voltage.

RS232 port interface lines fault protected to +/- 36V power on, +/- 40V power off.

Serial Port Isolation

2500V RMS port signal isolation per UL 1577.

3000V DC min. port to ground and port to logic power isolation.