The M4 -XPM series expansion I/O modules can serve in one of two capacities depending on where they are installed in the Metasys system. When installed on the Sensor/Actuator (SA) Bus of an equipment controller, an XPM expands the input and output interfaces that can be used with that equipment controller. When installed on the Field Controller (FC) Bus of a Metasys network engine , an XPM can be used as I/O point multiplexors to support monitoring and control from a Metasys network engine . The point multiplexor can also be useful for sharing points between other equipment controllers on the FC Bus using peer-to-peer connectivity. XPMs operate on an RS-485 BACnet MS/TP Bus and are BACnet Testing Laboratory (BTL) listed and certified to the BACnet Smart Actuator (B-SA) profile.