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.
A BACnet Router is the bus supervisor on an FC bus. The CH-PC controller is the bus supervisor on an SA bus. Bus supervisors have a fixed device address of 0 (zero) that cannot be changed (Figure 1). Depending on the model, a network sensor has a fixed address of 199 or an assigned (switch-selectable) address between 200 and 203. Table 1 provides a list of the valid MS/TP device address values and address value ranges for MS/TP devices.
Each MS/TP master 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.