User Manual

System configuration
Technical limits and limit values
22
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PX site
A Desigo PX automation system site.
The PX BACnet devices which control the plant in a PX site are interconnected
via the global objects and the primary copy procedure.
A PX site is independent of the limits affecting the BACnet network. A site can
extend over several BACnet networks. One BACnet network may include
several sites. All the associated limits must be maintained simultaneously.
A PX site cannot be extended beyond the limits of a BACnet internetwork. This
is particularly important in the case of BACnet PTP internetworks.
PX plant
A PX plant is part of a PX site and generally comprises several partial plants
(plant structure).
A PX plant can be distributed over several PX BACnet devices. In principle PX
BACnet devices can be distributed to different BACnet networks. However,
owing to the communications load between partial plants, this is not
recommended.
The plant structure is mapped to BACnet by means of hierarchy objects.
Operator units with generic operation automatically read this structure.
BACnet MS/TP
A BACnet MS/TP network is a BACnet network that is physically based on EIA-
485 and operated using a BACnet-specific MasterSlave/TokenPassing data link
protocol (see BACnet standard clause 9). An MS/TP network is linked via a
BACnet router to a BACnet/IP or BACnet/LonTalk network.
Desigo room automation
Includes the BACnet devices connected directly to BACnet/IP or BACnet
MS/TP, used for room automation.
These BACnet devices are not part of a PX site. There is no connection via
global objects and the primary copy procedure.
Desigo room automation system functions
In Desigo room automation, primary subsystem control functions are
centralized as Desigo room automation system functions.
PX system functions
A PXC.. of a PX site as PX system function can assume Desigo room
automation subsystem functions such as scheduling, life check, time
synchronization for a Desigo room automation system function group for
BACnet devices for room automation.
System function group
A Desigo room automation system function group cannot be identified or
defined via the network topology. Engineering the Desigo room automation
system functions of the PX system functions determines the Desigo room
automation system function group.
For more information, see chapter
System Overview and Network Architecture .
22.1 Technical limits and limit values
There are two types of limits:
● Technical limits (hard-coded limits) are maintained by technical means.
They cannot be exceeded.
● Recommended limits (soft limits) are not enforced by technical means.
They can be exceeded.