127
ECLYPSE APEX
See
for more information. The shield of one data bus must be
grounded at one point as specified in
Data Bus Shield Grounding Requirements
. The shields of the two
data buses must be connected together and 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 con-
nected 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). De-
vices on another Network can have the same MAC Address as messages are not passed at the
internetwork level using the MAC Address. The MAC Address also defines the devices on the data
bus that are Masters and Slaves, among other categories (see
). The MAC
Address is also used to share data bus bandwidth between devices through token passing be-
tween Master devices.
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The Device Instance uniquely identifies a device across the BACnet internetwork. The Device In-
stance is any number 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 mes-
sages 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.
Both the MAC Address and the Device Instance must be set for each device and are essential for
proper BACnet LAN operation.
For an example of how MAC address, Device Instance number, and Network Number apply to a typi-
cal BACnet network, see
Adopting a Numbering System for MAC Addresses, Device Instance Numbers,
.
About the MAC Address
The MAC Address is a number from 0 to 255; however, we recommend reserving some MAC Ad-
dresses for common commissioning and maintenance tasks. For example, when a portable adapter is
set to use one of these reserved MAC Addresses, it can be temporarily connected with certainty to
any BACnet MS/TP data bus of any site without conflicting with other devices already connected to the
BACnet MS/TP data bus. We strongly recommend that the MAC address of ECY Series Controller’s
MS/TP port be always set to 0.
MAC Addresses should be used as shown in the following table.
MAC Address
Value / Range
Usage
Devices
0
Data Bus Master (ECY Series Controller)
This address is invalid for Distech Controls’ ECB series
devices
1
Temporary commissioning connection
This address is invalid for Distech Controls’ ECB series
devices
2
Reserved
Other
3-127
Master Range
Master devices: All Distech Controls’ devices are
master devices and should be in this MAC Address
range
128-254
Slave Range
Slave devices and network sensors
255
Broadcast
Do not apply address 255 to any device
Table 15: Recommended BACnet MS/TP Bus MAC Address Values / Ranges for BACnet MS/TP Data Bus De-
vices
BACnet MS/TP Communication Data Bus Fundamentals
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