Issue
MSTP controllers go offline when changing the MaxMaster value in the Automation Server from it's default of 127
Product Line
EcoStruxure Building Operation
Environment
- Building Operation Workstation
- Building Operation Automation Server
- MSTP Master Controllers
Cause
The MaxMaster value is being set lower than some or all of the MSTP controllers on the network
Resolution
EcoStruxure Building Operation supports MSTP Master controllers in the address range 0-127 (often refered to as the node id). The MSTP network is a token passing network where the token is passed around the network, until a controller has the token it cannot 'talk' to other devices.
The MaxMaster value is defaulted to 127 to allow all devices on the network to receive the token and reply to online status requests, send values etc. If the MaxMaster value is less than any of the MSTP Master controller addresses then those controllers never receive the token and cannot respond to online status requests.
The value for the MaxMaster needs to be equal to or greater than the highest addressed MSTP controller node id. For example, if the highest node id=54 then the MaxMaster will need to be set to 54 or higher. For maximum efficiency the MaxMaster should be set 1 or 2 greater than the highest controller address, this allows for adding future devices without needlessly polling for many non-existent devices.
Please refer to BACnet MS/TP Network Properties – Basic Tab or Configuring the MS/TP Network for b3 Communication
