Distech ECYPSE - Maximum Number of Bacnet MS;TP Devices on a Data Bus Segment and Baud Rate; Data Bus Segment MAC Address Range for Bacnet MS;TP Devices; Maximum Number of Bacnet MS;TP Devices on a Data Bus

BACnet MS/TP Communication Data Bus Fundamentals
112 ECLYPSE User Guide
Maximum Number of BACnet MS/TP Devices on a
Data Bus Segment and Baud Rate
The following technical parameters limit the number of devices on a BACnet MS/TP Data
Bus Segment.
 The BACnet MS/TP Data Bus Segment has a hard limit on the number of devices that
can communicate due to the device addressing scheme (the MAC Address Range for
BACnet MS/TP Devices). See Data Bus Segment MAC Address Range for BACnet
MS/TP Devices on page 112.
 Each device presents an electrical load on the BACnet MS/TP Data Bus Segment. This
is called device loading. The number of devices that can be connected to a BACnet
MS/TP Data Bus Segment is limited by the loading of each device. See Device Loading
on page 113.
 Choosing a low baud rate can cause BACnet MS/TP Data Bus congestion that can limit
the amount of data that can be efficiently exchanged between devices connected to the
BACnet MS/TP Data Bus. For example, at 9600 baud, the maximum number of devices
is reduced to 25 due to the increased time it takes for token passing between devices.
The recommended baud rate is 38 400. See Baud Rate on page 113.
 Distech Controls recommends that you connect no more than 50 of our ⅛ or ½-load
devices on a single BACnet MS/TP Data Bus Segment when a baud rate of 19 200 or
higher is used (preferably 38 400 baud). This is to ensure that the BACnet MS/TP Data
Bus has enough bandwidth to efficiently communicate network variables between
controllers.
These parameters are described in greater detail below.
Data Bus Segment MAC Address Range for BACnet MS/TP
Devices
The BACnet MS/TP data bus supports up 255 devices:
 Up to 128 devices (with device MAC addresses in the range of 0 to 127) that are
BACnet MS/TP Masters (that can initiate communication).
 Up to 128 devices (with device MAC addresses in the range of 128 to 255) that are
BACnet MS/TP Slaves (cannot initiate communication).
However, it is recommended that any given data bus segment have no more than 50
devices, when a baud rate of 19 200 or higher is used for the BACnet MS/TP Data Bus. A
repeater counts as a device on each data bus segment to which it is connected.
All Distech Controls’ devices are categorized as BACnet MS/TP Masters, that is, their device
MAC address can be set in the range of 0 to 127 only.