User Manual

Network architecture
BACnet architecture (MLN & ALN)
14
198 | 351 CM110664en_07
● 0-127 reserved for master devices
● 0-254 reserved for slave devices
● 255 reserved for broadcasts
The MAC address can be set via DIP switch (hardware) or related configuration tools (software) for each
device.
Structuring
MS/TP is transmitted via two-core cables as per EIA-485/RS-485. The maximum length of a segment is
1200 meters. 64 devices are allowed on a segment.
Different segments can be interconnected via repeaters to form a larger EIA-485-network. The specific
electrical properties, such as polarity, common signal ground, terminating resistances, etc. must be taken
into account. The actual, possible network size and maximum transmission rate primarily depend on the
network structure. Establishing a network in daisy chain form is best.
Due to relatively difficult, electrical conditions imposed by EIA-485 wiring and limited data transmission
capacity, we recommend using BACnet MS/TP only for devices with low data volumes that are
geographically far apart.
For devices with larger data volumes and shorter distances to the Desigo automation station, integration in
Desigo primarily should be carried out via TX Open or PX Open.
System devices
PXG3 is a BACnet router that routes BACnet telegrams between BACnet networks and different data link
layers. It is available in two versions:
● PXG3.L: (triangle router) Simultaneous routing between Ethernet/IP, LonTalk, and MS/TP
● PXG3.M: Routing between Ethernet/IP and MS/TP
See
BACnet router for BACnet/Ethernet/IP, BACnet/LonTalk, BACnet MS/TP PXG3.L, PXG3.M
(CM1N9270).
An individual BACnet IPv6 data link can be used as an option for the router. As a result, the PXG3.M is
turned into a triangle router and the PXG3.L to a square router. The router can be configured either via
XWP or the integrated web server.
BACnet address
Every BACnet device in the BACnet internetwork can be accessed via its BACnet address.
The BACnet address is defined by the BACnet standard and comprises the following elements:
Designation Description
Network number Network number of the BACnet network in which the device is located. The network number is
only parameterized on devices with BACnet router functionality (including half router) and is
implicitly valid for all BACnet devices in the BACnet network.
BACnet MAC address Address specific to the transport protocol. This address is written to the device in the
commissioning phase.
BACnet MAC address for:
LonTalk: 2 octets, subnet ID und node ID
IP: 6 octets, IP address and UDP port
IPv6: 3 octets as virtual MAC address (VMAC)
BACnet/IP
MS/TP
. . .
DXR2 DXR2 DXR2
DXR2
Router
PXG3
10664Z42_06