Bacnet Interface; Bacnet Bus Topology; Line Termination Resistors; Bias Resistors - Grundfos CIU 300 Functional Profile And User Manual

3. BACnet interface

3.1 BACnet bus topology

The Grundfos CIM/CIU 300 is connected as a BACnet MS/TP master
directly to the BACnet MS/TP network.
Master
Slave
LT
BR
Master
LT = Line Termination
BR = Bias Resistors
Fig. 2 Example of BACnet MS/TP network
BACnet MS/TP is a multi-master system, meaning that there can be
more than one master on the network. It uses a token to control
access to the bus network. A master node may initiate the
transmission of a data telegram when it holds the token. Both
master and slave nodes may transmit data telegrams in response to
requests from master nodes, but slaves never hold the token.
Master nodes pass the token between them.
A BACnet MS/TP segment is a single contiguous medium to which
BACnet nodes are attached. Segments can be connected by use of
repeaters or bridges, thus forming networks.
Multiple networks may be interconnected by BACnet routers to
form a BACnet inter-network.

3.1.1 Line termination resistors

Line termination must be connected at each of the two ends of the
segment medium. The CIM/CIU 300 has optional line termination
resistor on board.

3.1.2 Bias resistors

At least one set, and no more than two sets, of network bias
resistors must exist for each segment so that an undriven
communications line will be held in a guaranteed logical one state.
The bias provides a reliable way for stations to detect the presence
or absence of signals on the line. An unbiased line will take an
indeterminate state in the absence of any driving node.
The CIM/CIU 300 has no bias resistors.
6
Slave
Master
LT
Slave
Slave