BACnet MS/TP Communication Data Bus Fundamentals
ECLYPSE User Guide 117
the BACnet MS/TP data bus and an ECY Series Controller at the other end, you must set
the built-in EOL termination in the ECY Series Controller so that proper biasing is provided to
the BACnet MS/TP data bus.
ECY Series
NET-
NET +
S
Typical
BACnet
Device
First and last daisy-chained device:
- EOL Terminations are ENABLED
at one end, and EOL resistor is
installed at other end.
All other Devices:
- EOL Terminations are DISABLED.
NET+
NET-
Typical
BACnet
Device
NET+
NET-
Typical
BACnet
Device
NET+
NET-
Typical
BACnet
Device
NET+
NET-
No Built-in EOL
Termination
Data Bus: Shielded Twisted Pair Cable
No Built-in EOL
Termination
No Built-in EOL
Termination
No Built-in EOL
Termination
EOL: Add a 120
Ohm resistor as
shown here
120
Ω
EOL ENABLED: Use the
ECY-S1000 as a first or
last daisy-chained
device: The internal EOL
Termination MUST be
set to ON to provide bias
to BACnet MS/TP Data
Bus
Electrical
System
Ground
Figure 11-3: Typical EOL Terminations with BACnet MS/TP Thermostats with
Biasing Provided by the ECY Series Controller’s Built-in EOL Termination set to
ON
About Setting Built-in EOL Terminations
ECY Series Controllers have built-in EOL terminations. These Controllers use jumpers to
enable the EOL resistors and biasing circuitry.
ECB-PTU Series Line-Powered Controllers use DIP switches (found alongside those DIP
switches used to set the MAC address) to enable the build-in EOL resistors and biasing
circuitry.
ECB Series 24V-Powered Controllers have built-in EOL terminations. These Controllers
use jumpers to enable the EOL resistors and biasing circuitry.
Refer to the controller’s Hardware Installation Guide for how to identify and set a controller’s
built-in EOL terminations.
Only a Daisy-Chained Data Bus Topology is Acceptable
Use a daisy-chained BACnet MS/TP data bus topology only. No other data bus topology is
allowed.
Maximum of 32 nodes and 1200 meters.
Maximum is 50 nodes when using
Distech Controls devices exclusively
MS/TP Data Bus Segment
Central Plant Air Handling Controllers
Ethernet, TCP/IP, BACnet/IP, LONWORKS IP, XML, HTTP, oBIX
- Alarm
- Trend Log
- Schedule
EC-Net
AX
Supervisor
- Data Bus Management
- Data Bus Integration
- Device Configuration and
programming
- Graphical Interface
Configuration
EC-Net
AX
Pro Web Browser
- User Interface
- Remote Access
- Embedded EC-Net
AX
Pro
Segment 1
ECY-S1000
EOL Internally Set
EOL
ON
EOL Internally Set
EOL
ON
Figure 11-4: Typical BACnet MS/TP LAN Topology Showing How Devices are
Daisy-Chained Together to Form One Data Bus Segment
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