XPM
Input/Output Expansion Module. The Metasys XPM series products are input and output expansion modules with integral RS-485 MS/TP communications.
When you install an XPM on the Sensor/Actuator (SA) Bus of an equipment controller, the XPM expands the number of Input/Output (I/O) points that are connected to an equipment controller. When you install an XPM on the Field Controller (FC) Bus of a Metasys network engine, you can use the XPM as an I/O point multiplexor to support monitoring and controlling from a Metasys network engine.