SXWASPXXX10001 AS-P BACnet MS/TP Connection Issue

[thunderbolt_developer]

Hello everyone,

We are a company that provides building automation and air conditioning solutions to our customers.

We received a serious BACnet communication issue feedback from our customer regarding one of our products. Here, our customer's problem is that the Schneider brand SXWASPXXX10001 AS-P model upper automation device and your products' BACnet communication, after 2-3 child devices, the device with the lowest BACnet mac address on the line constantly enters the packet transmit loop. This device continuously transmits the Poll for Master BACnet message packet to the line.

We are investigating a solution to this problem. But we did not understand.

Thanks for the solution in advance.

[CraigEl]

This is because you have not set the MSTPMaxMaster property in all of the devices. This should generally be set to a number 1 or 2 higher than the highest MAC address on the bus.

In BACnet MSTP, every 50 token passes, the highest addressed device does a poll for master to check that no new devices have been added to the network. If the MSTPMaxMaster setting is left at the default 127 then it will poll the network for all MAC addresses up to this number. Setting the MSTPMaxMaster to 1 or 2 higher than the highest address on the bus allows for new devices or interfaces to be added and enter the token passing without undue time taken with poll for master on addresses that don't exist.