When should the MSTP bias resistors be enabled on a MNB-1000?

Issue

When should the MSTP bias resistors be enabled on a MNB-1000?

Product Line

TAC I/A Series

Environment

BACnet /MSTP trunk under an MNB-1000

Cause

RS-485 biasing rules apply to BACnet / MSTP

Resolution

An MSTP network requires at least one set of bias resistors but no more than two sets. If a UNC device exists on the network it will provide one set of resistors.  No others are needed. If one or more MNB-1000s are on the network, enable only one set of bias resistors.