User Manual

Network architecture
BACnet architecture (MLN & ALN)
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For each PTP connection in Desigo CC, only the telephone number needs to be
defined.
Data link layer MS/TP
Data Link Layer Master/Slave Token Passing MS/TP is another protocol
variant for BACnet. Desigo supports this variant via a specific router that
connects BACnet MS/TP to BACnet/IP.
MS/TP is based on the physical layer EIA-485/RS-485 and supports baud rates
up to 76.8 kbps. Up to 256 devices can be connected to one MS/TP segment (in
theory, dependent on their unit load).
Each device has its own unique MAC address. The MAC address is one octet
long and defined as follows:
● 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.
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.
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
Application Layer
Network Layer
PTPIPLonTalk MSTP
BACnet/IP
MS/TP
. . .
DXR2 DXR2 DXR2
DXR2
Router
PXG3
10664Z42_06
Addressing MS/TP
devices
Structuring
System devices