Point Attribute Mapping

If you want to export more then the essential C-Bus attributes to BACnet, you must explicitly enable this option. First, you have to globaly activate the mapping feature in the menu Preferences -> C-Bus -> Map C-Bus Attributes (see chapter Configuration). In Point Manager, you must select the points for which you want to map additional attributes. Afterwards, click on the Options button and in the pop-up window, select the attributes you wish to apply.

Save the changes with the Save button.

If you decide to export additional data point attributes to BACnet, then the C-Bus traffic considerably increases, which affects the performance of the entire gateway. Because there is no Refresh / Change of Value Push mechanism for the C-Bus attributes, the attribute values must be polled and response time to BACnet requests increase. Even C-Bus problems may occur.

The behaviour of the gateway when exporting additional attributes is mainly affected by the behaviour of the BACnet client and is strongly dependent on the building automation system provider. Some implementations send the requests very selectively and require only the data processed by the system. Other systems boost demand for all objects with all properties and eventually even several times per second, which exceeds the capabilities of the C-Bus. To avoid the C-Bus overloading the gateway does not support BACnet feature ReadPropertyMultiple when the option Map C-Bus Attributes is active.

Attributes Mapping

The following table shows the mapping between the C-Bus attributes and BACnet properties.

• Note: BACnet knows two different limit-enable properties. To change the C-Bus attribute SUPPRESS_ALARM, both BACnet limit-enable properties (hi/lo) must be set identically, e.g either both are true or all are false.

• If the attribute mapping is generally disabled or if the point attribute TREND_HYSTERESIS is not enabled for export into the BACnet, the value of the property cov-increment is set to 0.0. A not null value of cov-increment is the prerequisite for the activation of the COV subscribe service.

Some of the BACnet properties have gateway specific proprietary ID: