L-Gate User Manual 59 LOYTEC
Version 3.2 LOYTEC electronics GmbH
network variable. Acknowledging alarms in the alarm server is adhering to the LONMARK
specification and relies on the RQ_CLEAR_ALARM mechanism.
5.5.5 Limitations for Local CEA-709 Trends
Local CEA-709 trend objects support trending multiple data points in all trend modes,
interval, COV, and trigger. The enable data point is also supported. All data points can be
NVs, registers or of any other technology. There is no L
ONMARK object linked to the trend
object. Consequently, trend data cannot be accessed over a L
ONMARK mechanism.
5.6 BACnet Technology
5.6.1 BACnet Data Points
Data points in the BACnet technology are known as BACnet objects. They have a specific
type (e.g. analog input or binary output) and a set of properties, which describe the data
point more closely. The actual value is stored in the “Present_Value”.
On the device, there exist two classes of BACnet data points:
• BACnet server objects (SO): These BACnet objects configured by the Configurator
software to be allocated locally on the device. These objects can be accessed by the
BACnet building control system or operating workstations. They support COV
subscriptions to deliver value changes in an event-driven way.
• BACnet client mappings (CM): For certain applications, it is necessary that the
device acts as a BACnet client. This functionality can be configured by activating a
client mapping. Client mappings can be of the type Poll, COV, Write, or Auto. This
specifies how the BACnet client accesses other BACnet objects on the BACnet
network. The Auto method determines the best way (poll, COV, or write) to talk with
other server objects. Poll is used for objects that need to read data from other BACnet
objects in a periodic manner. COV is used to subscribe for COV at other BACnet
objects in order to get updates in an event-driven fashion. Write is used to send updates
to other BACnet objects.
The direction of BACnet server objects deserves a closer look. The direction specified for
data points in the Configurator software always refers to the network view of the
communication. The definition of input and output objects in BACnet, however, refers to
the process view, which is opposite to the network. Therefore, a BACnet analog input (AI)
object is modeled as an analog output data point. The direction of client mappings naturally
refers to the network communication. Therefore, a write client mapping is represented as an
analog output data point.
In BACnet commandable objects can be written with values at a certain priority. The value
with the highest priority is in effect. When revoking a written value, the NULL value is
written. This takes back the value. When all written values are withdrawn, the
Relinquish_Default value is in effect.
The default value feature of a data point is mapped to the Relinquish_Default property for
commandable objects. For BACnet objects, which are not commandable, the
Present_Value is initialized with the specified default value.
5.6.2 BACnet Alarming
BACnet alarming on the device is based on the intrinsic reporting mechanism. Currently,
algorithmic reporting is not supported. Alarm conditions can only be applied to data points,
which map to BACnet server objects. If defined, the intrinsic reporting properties of the
underlying BACnet objects are enabled. Alarm conditions can be specified for analog
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