Specifications

FC Bus
An FC bus connects a Metasys® system NAE or NCE to FACs, FECs, VMA16s, IOMs, and TEC26xx Series
thermostats. Third-party BACnet MS/TP devices can also be connected to the FC bus.
Figure 1: Example of an MS/TP Communications Bus
On an FC bus, the NAE or NCE is the bus supervisor. An FC bus supports up to three bus segments that are
connected with network repeaters (Figure 9). See Local FC Bus Rules and Specifications for more information.
SA Bus
The SA bus connects NCEs, FACs, FECs, and VMA16s (field controllers) to end point devices such as IOMs, network
thermostats, network sensors, and Johnson Controls Variable Speed Drives (VSDs).
On an SA bus, an NCE, FAC, FEC, or VMA16 is the bus supervisor. The SA bus is a private MS/TP bus that only
supports those devices that can be defined using the CCT programming tool. The bus does not support bus segments
(Figure 11). See SA Bus Rules and Specifications for more information.
6MS/TP Communications Bus Technical Bulletin