Distech Controls ECB-VAV, User Manual

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BACnet MS/TP Communication Data Bus Fundamentals
Network Guide 31
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 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
Table 7 ). The MAC Address is also used to share data bus bandwidth between
devices through token passing between Master devices.
• The Device Instance uniquely identifies a device across the BACnet internetwork. The
Device Instance 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 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.
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 typical BACnet network, see
Figure 22 .
About the MAC Address
The MAC Address is a number from 0 to 255; however we recommend reserving some MAC
Addresses for common commissioning and maintenance tasks. For example, when a portable
adaptor 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 each MS/TP port of an EC-BOS be always set to 0.
MAC Addresses should be used as shown in the following table.
Table 7: Recommended BACnet MS/TP Bus MAC Address Values / Ranges for BACnet MS/TP Data
Bus Devices
MAC Address
Value / Range
Usage Devices
0 Data Bus Master
(Building Controller) EC-BOS
This address is invalid for Distech Controls'
ECB devices