Issue
How does BACnet point mirroring (COV subscription) work when the source BACnet controller is offline.
Environment
- CyberStation
- BACnet controllers
Cause
Obtain information about the functionality of COV subscription when BACnet controller is offline.
Resolution
When you mirror a BACnet point between BACnet controllers via a pulling PE program using the (local point = remote point) syntax or the ReadProperty() function, Continuum subscribes the information in the COV Subscription Table of the source controller.
Once the COV subscription is set up, low-level embedded code in the source controller checks the current value of the point and compares it to the COV Increment. When it finds the change is greater than the COV increment value, the source controller transfers the new value to the destination controller.
In the destination controller, low-level embedded code receives the value from its transceiver buffer and writes it to its local memory.
And now, the pulling PE program reads the value from the local memory and updates the value to the point object.
As a result, the pulling PE program in the destination controller still reads the last value from its local memory even if the source controller goes offline. This functions the same way as the standard Continuum import/export.
