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7-0 Communication Protocols
7-1 BACnet MS/TP
Communications Wiring
For optimal performance, use 24 AWG (0.65 mm) stranded, twisted pair
shielded cable. The BACnet MS/TP communication wire is polarity sensitive
and the only acceptable topology is to daisy-chain the cable from one
controller to the next.
•
The first and last daisy-chained BACnet MS/TP devices must have
their EOL resistors enabled / installed. All other devices must have
their EOL resistor disabled (default factory setting). See Figure 16
below.
•
The first and last daisy-chained BACnet MS/TP devices 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.
•
Isolate all shields with electrical tape so there is no exposed
metal that can touch ground or other conductors.
•
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 BACnet MS/TP data bus.
Use the Server Module's RS-485 port to connect to a trunk of BACnet MS/TP
devices. This port must be configured in the controller's Web interface prior
to use.
Server
Figure 16: BACnet MS/TP Communications Wiring
When inserting multiple wires into a terminal-block connector, ensure to
properly twist wires together prior to insertion.
7-2 Modbus RTU
Communications Wiring
BACnet MS/TP and Modbus RTU communications are made by connecting
directly to separate RS-485 ports.
Furthermore, Modbus TCP devices can be integrated by connecting them to
the controller's IP network.
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7-2 Modbus RTU
Communications Wiring - cont'd
For optimal performance, use 24 AWG (0.65 mm) stranded, twisted pair
shielded. 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 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). See Figure 17
below.
•
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 conductors.
•
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 the Server Module's RS-485 port to connect to a trunk of Modbus RTU
devices.
Server
Figure 17: Modbus RTU Communications Wiring
If inserting multiple wires in the terminals, ensure to properly twist wires
together prior to inserting them into the terminal connectors.
7-3 Modbus TCP
Communications Wiring
Connect Modbus TCP devices to the same IP subnet the controller is using.
This connection can be made by connecting the Modbus TCP device to an
Ethernet port on the Server Module with a Cat5e network cable for example
(see Wired Connection).
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