Distech Controls ECLYPSE Installation Manual page 19

Use any RS-485 port to connect to a trunk of BACnet MS/TP devices. RS-485 port terminal connectors are labeled such that NET+ is the same as + and
NET- is the same as -. This port must be configured in controller's Web interface prior to use.
Figure 26: BACnet MS/TP Communications Wiring
When inserting multiple wires into a terminal-block connector, ensure to properly twist wires together prior to insertion.
Modbus RTU Communications Wiring
BACnet MS/TP and Modbus RTU communications are made by connecting directly to separate RS-485 ports. The Connected Equipment Controller inte-
grates up to three RS-485 ports when equipped with one ECY-RS485 extension module allowing the controller to support more than one trunk or com-
munication protocol at a time.
Furthermore, Modbus TCP devices can be integrated by connecting them to the controller's IP network.
The ECLYPSE User Guide provides extensive information and requirements to implement a Modbus RTU network. It contains information about network
topology, network and sub network wire length restrictions, cable type, device addressing, etc. It can be downloaded from our website. For optimal per-
formance, use Distech Controls 24 AWG (0.65 mm) stranded, twisted pair shielded cable or refer to the ECLYPSE User Guide for cable specification.
The Modbus RTU communication wire is polarity sensitive and the only acceptable topology is to daisy-chain the cable from one controller to the next.
The ECLYPSE User Guide can be downloaded from our website.
As shown in the figure below:
£ The first and last daisy-chained Modbus RTU devices must have their EOL resistors enabled / installed. All
other devices must have their EOL resistor disabled (default factory setting).
£
The first and last daisy-chained BACnet MS/TP device must have their BIAS enabled. All other devices
must have their BIAS disabled (default factory setting). See the figure below. Note that the BIAS settings for
BACnet MS/TP controllers that do not have a specific setting to enable / disable BIAS usually means that
the BIAS is enabled when the EOL resistors are enabled.
£
When the Modbus RTU data bus is connected to a following device, twist data bus shields together.
£ Isolate all shields with electrical tape so there is no exposed metal that can touch ground or other conduc-
tors.
£ The shield of the data bus must be connected to the electrical system ground at only one point – usually at
one end of the bus as shown below.
£
Connect no more than 50 devices to a Modbus RTU data bus.
Use any RS-485 port to connect to a trunk of Modbus RTU devices. RS-485 port terminal connectors are labeled such that NET+ is the same as + and
NET- is the same as -.
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