What is BACnet MS/TP?
By Bassirou Thiam, building automation engineer · Updated
BACnet MS/TP (master-slave/token-passing) is the BACnet data link that runs over RS-485 twisted pair, used for field controllers on each floor or system. Master devices pass a token to take turns on the wire. Each trunk connects to the IP backbone through a router.
Limits that shape the design
- MAC addresses 0 to 127 for masters, unique on the trunk;
- no more than 32 devices and 4,000 ft per segment without a repeater;
- around 60 devices per network in practice, depending on traffic;
- end-of-line termination at both ends, shield grounded at one end.
Details: BACnet addressing.
Sources
Related
GlossaryWhat is an MS/TP MAC address?Definition of the BACnet MS/TP MAC address: the device address on its RS-485 trunk, valid ranges for masters and slaves, and Max Master.
GlossaryWhat is BACnet/IP?Definition of BACnet/IP: BACnet carried over Ethernet and IP networks, used for the backbone between building controllers and the front end.
GuidesBACnet device instance numbering and MS/TP addressingThe rules for BACnet device instances, MS/TP MAC addresses, Max Master and network numbers, with segment limits and a numbering scheme you can reuse.