Each device connection on an MS/TP bus requires a device address to coordinate communication. Each bus has a set of device addresses that is separate and independent from the device addresses on all other buses. Devices connected to both an MS/TP bus and SA bus have two device addresses, one for each bus connection (Figure 1).
In the MS/TP bus hierarchy, device connections on separate buses can have the same device address. For example, every bus supervisor connection on an MS/TP bus has a device address of 0 (zero), and the device address for the first network sensor on any SA bus is 199. This is possible because separate buses are identified with different network numbers. Figure 1 shows a simple example of an MS/TP bus and the device addresses for connections on the FC bus and SA bus.
An NAE, NCE, SNE, SNC or BACnet Router is the bus supervisor on an FC bus (or Remote Field Bus). The CGM, CVM, FAC, FEC, VMA, or the integral field controller on an NCE or SNC is the bus supervisor on an SA bus. The supervisory devices have a default address of 0. Bus supervisors have a fixed device address of 0 (zero) that cannot be changed (Figure 1). The current range of network sensors are all addressable with the DIP switch set from 199 to 206 and the factory set at 199. Table 1 provides a list of the valid MS/TP device address values and address value ranges for MS/TP devices.
Each MS/TP manager controller passes the token to the controller with the next known address. After 50 token passes, each controller searches for other controllers that might have joined the network by attempting to send the token to the controller with the next consecutive address, starting with one higher than its own, until one is found. While you do not need to address devices on the trunk consecutively, you can improve performance by minimizing address skipping. To help with address value selection, see Table 1.