Device Addressing - Acuity Controls nLight ECLYPSE User Manual

BACnet MS/TP Communication Data Bus Fundamentals
Typical BACnet Device
EOL ON
1
Data Bus: Shielded
Twisted Pair Cable
Figure 99: Repeater Connections when it is the First or Last Device on its Respective Data Bus Segment
The BACnet MS/TP Data Bus must be biased. This bias can only be provided by built-in EOL termination resistors (ones
set with a jumper or DIP switch). When a repeater is the first or last device on its respective data bus segment, use the fol-
lowing methods to provide MS/TP Data Bus biasing and EOL termination as applicable to your situation:
1. On the BACnet MS/TP data bus segment ❶ shown in the above figure, bias and EOL termination is provided by a con-
troller's built-in EOL termination being set to ON. In this case the connection to the repeater cannot be more than 7.6
meters (25 feet) from this controller.
2. On the BACnet MS/TP data bus segment ❷ shown in the above figure, a 120Ω EOL Termination resistor is added to
the repeater's terminals. Biasing for this BACnet MS/TP data bus segment is provided by the built-in EOL termination
being set to ON at the last controller at the other end of this data bus.
See When to Use EOL Terminations
specified in Data Bus Shield Grounding
isolated with electrical tape as shown in the above figure. Refer to the controller's Hardware Installation Guide for how to
identify and set a controller's built-in EOL terminations.

Device Addressing

Device addressing allows the coordinated transfer of messages between the intended devices on the BACnet MS/TP data
bus and with devices connected to the internetwork. For this, each device connected to the BACnet MS/TP data bus is
identified by a MAC address, a Device Instance number, and a Network Number:
The MAC Address uniquely identifies a device on a Network (identified by a Network Number). Devices on another
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Network can have the same MAC Address as messages are not passed at the internetwork level using the MAC Ad-
dress. The MAC Address also defines the devices on the data bus that are Masters and Slaves, among other cate-
gories (see About the MAC
through token passing between Master devices.
The Device Instance uniquely identifies a device across the BACnet internetwork. The Device Instance is any number
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between 0 and 4 194 303. It is with the Device Instance that messages are exchanged between BACnet devices. The
Device Instance is also used by routers to forward messages to devices located elsewhere in the internetwork. Unlike
a MAC Address, a Device Instance cannot be reused elsewhere in the BACnet internetwork (it must be unique for the
entire network).
The Network Number is any number between 1 and 65 534. A network number identifies a LAN for routing purposes.
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Both the MAC Address and the Device Instance must be set for each device and are essential for proper BACnet LAN op-
eration.
For an example of how MAC address, Device Instance number, and Network Number apply to a typical BACnet network,
see Adopting a Numbering System for MAC Addresses, Device Instance Numbers, and Network
nLight ECLYPSE
BACnet MS/TP data bus
Bias and EOL termination is
provided by this controller's
internal EOL Termination
being set to ON
Data Bus Shields: Twist
together and Isolate with
electrical tape
Repeater
Data + (1) Data + (20)
Data – (2) Data – (19)
< 7.6 m
< 25 ft
for more information. The shield of one data bus must be grounded at one point as
Requirements. The shields of the two data buses must be connected together and
Address). The MAC Address is also used to share data bus bandwidth between devices
BACnet MS/TP data bus
Typical
Bias and EOL termination is
BACnet
provided by this controller's
Device
internal EOL Termination
No Built-in EOL
being set to ON
Termination
Data Bus Shields: Twist
together and Isolate
with electrical tape
The data bus shield must be connected to the electrical system ground at
one point only – usually at the Building Controller, when present
Typical BACnet Device
EOL ON
2
Numbers.
100