The whole C-Bus is treated as a one BACnet device. From the client side you can update the BACnet device properties Name and Description. All other device properties are currently read-only. This can be changed in future releases.

C-Bus data points are exported as BACnet value objects. Analog C-Bus points are mapped as BACnet Analog Value (AV) objects, digital C-Bus points are mapped as Digital Value (DV) objects. There is no special mapping for Input and Output points. All BACnet points are commandable. However, only the priority 8 (manual-operator) is allowed to write a new present-value. This can be changed in the BACnet preferences, see the parameter Manual level. BACnet points support COV subscription.

C-Bus Attributes and BAcnet Object Properties

While C-Bus data points are comparable to BACnet point objects, C-Bus point attributes correlate to BACnet point properties. The following table shows the mapping of essential attributes between C-Bus and BACnet. These attributes are discovered while commissioning the gateway and periodically refreshed in runtime.

C-Bus point attribute BACnet point property Writable
NAME object-name true
VALUE present-value true
DESCRIPTOR description true
ALARM_STATUS event-state false
OPERATING_MODE proprietary-2048 false
UNIT (analog point) engineering-unit true
UNIT (digital point) inactive-text, active-text true
TECHNICAL ADDRESS proprietary-2054 false
- reliability, status.fault false
Writing Point Value

To override the point value, you need to write the new value to the commandable level. Default level is 8 and can be changed in the BACnet preferences. When written, the gateway switches the C-Bus point mode into Manual and writes the new C-Bus point value.

To return to Auto mode, you need to write a NULL value to the commandable level. When written, the gateway switches the C-Bus point mode into Auto.

Time Synchronization

The gateway uses BACnet protocol to synchronize the date/time between the central building automation system and the C-Bus controllers. The BACnet service UTCTimeSynchronization sets the time in all controllers where the BACnet mapping is enabled. Controllers not enabled for BACnet export are not synchronized.