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Adding BACnet client functionality

Goal is to configure a second AC500 controller as BACnet client which reads an analog value from a server. This example is according to Fig. 280 BACnet objects, properties, services and BIBBs, right part.

  1. Add a new controller and configure a “BACnet Server” root object according to ⮫ “Configuration of BACnet server root object ”.

  2. Set ‎InstanceNumber‎ to ‎14‎ and ‎InstanceName‎ to ‎Device 14‎.

    BACnet_Device14

  3. In addition to BACnet objects, BACnet clients can also be inserted as devices under a “BACnet Server”. Add a “BACnet Client Read Property” below the “BACnet Server” node.

    BACnet_Client_Read

  4. The created object “BACnet Client Read Property” generates a function block instance which can be used to program the client read functionality. The figure below shows a simple example.

    In line 1-5 of the code part the function block is called with the following parameter:

    • Device ID of the server to read from (‎12‎) ⮫ “Supported objects and properties ”

    • Object ID of the object to read from (‎1010‎ for the “Analog Input”)

    • Object type (“Analog Input”)

    • Property to read (“present value”)

    • ‎triggerRead‎ to start the read operation

    When the user (or another program part) sets the variable ‎triggerRead‎ from ‎FALSE‎ to ‎TRUE‎ the edge triggered function block ‎BACnet_Client_Read_Property‎ starts operation and sends the read request to the server device. After receiving the reply from the Server, the output ‎.xDone‎ gets ‎TRUE‎ (line 8) and the temperature value can be read from the output ‎.result‎ (line 14).

    BACnet_Client_Read_Property

  5. Download this program to another AC500 controller, which is in the same IP network as the server. Set it to run and read the temperature value by setting ‎triggerRead‎ to ‎TRUE‎. In online mode the read temperature value can be observed in line 14.

    BACnet_Client_Read_Line14

Alternative configuration

Unlike BACnet objects, a BACnet client does not require a complex (static) configuration, thus a client function block can be used without creating a BACnet client as device.

BACnet_Client_Device

There is no ‎BACnet_Client_Read_Property‎ object created below the “BACnet Server”. Instead a function block ‎BACnet_Client_Read_Property‎ must be declared in the PRG (line 6 in the declaration) and initially "connected" to its “BACnet Server” in IEC-code via ‎RegisterToServer()‎, and thus get activated (line 2 in the code) ⮫ “Reference, function blocks”.

BACnet_Library