What is the purpose of the MAX Master on a BACnet trunk?

The MAX Master is used to reduce the Who-Is process time. A BACnet branch may only have 6 devices yet the Who-Is frame will search out until all 127 MAC addresses have been queried. Only device containing the MAX Master will terminate the search before querying all the way to MAC address 127. Best practice is to set the MAX Master in the device with the highest MAC address. By creating a MAX Master of 2-4 greater than the highest assigned MAC address, the Who-Is search will stop at the MAX Master, but this still leaves room for a few more devices to be added to the branch if necessary.

The maximum number for MAC addresses is 127 for a BACnet branch.

Setra's FLEX Room Monitor has the option to select a MAX Master.