User Manual

BACnet networks with MS/TP trunks

Diagnostics and troubleshooting in BACnet networks with MS/TP trunks

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Faults Possible causes & troubleshooting

Communication is slow. ● A master device normally holds the token for only a few milliseconds, with the

forwarding to the next device taking up to 250 ms. In other words, a high

number of devices causes a high cycle which requires a very conservative

(long) timeout value. You must configure the following timeouts if MS/TP

devices participate in the communication:

– APDU timeout: 6000 ms

– APDU segment timeout: 5000 ms

– Max Info frames: 50

● Operation on the Desigo CC management platform requires, where there are

lots of BACnet MS/TP devices, reading the functions sequentially by

discipline. This requires training course and operator instructions.

Communication no longer restarts after a power

outage or communication no longer starts after

a power outage on the BACnet/IP router.

● Communication – Data traffic is too high or way too high. In other words,

reduce or cease the following:

– Room segment communication

– No lighting or blinds application

– Max. one Desigo CC management platform

– Max. 5 trends per room

– Max. 3 alarms per room

– No central functions for gathering, i.e. for the hot water supply chain,

chilled water, air

BACnet networks ● PXG3.M runs automatic network checks, and indicates errors with an

illuminated Info-LED.

● PXG3.M operates on large projects as BBMD. These devices must have a

fixed IP address and not DHCP.

● Only one PXG3.M with BBMD functionality permitted per BACnet network.

Have you considered notes from technical

documentation?

●

Desigo Ethernet, TCP/IP, MS/TP and BACnet fundamentals

(CM110666)

●

Desigo room automation engineering, mounting and installation

(CM111043,

Section

Network topology

)