Networking Options
The standard FAC-2100 provides hardware support for networks compatible with RS-232, RS-422, and RS-485 voltage levels.
...
RS-485 networks should be wired in a straight-line bus with biasing and terminated at the two ends. Termination resistors should match the characteristic impedance of the transmission line (typically 120 ohms). Note that the FAC-2100 has internal dip switches that can activate built-in 120 ohm termination resistors.