BACnet: Cyclic Reading of a Property

Hardware

• Raspberry Pi as a BACnet server (provides data points)
• CODESYS Control Win V3 as a BACnet client (cyclic reading of the data points)

Requirements for the server and client

Check that the following entries are present in the file CODESYSControl.cfg.

• Including the BACnet component:
  [ComponentManager]
  Component.[n+1]=CmpBACnet

• Including the INI file of the BACnet stack (pay attention to the syntax):
  [CmpBACnet]
  IniFile=bacstacd.ini

Requirements for the BACnet server

• Create a "Standard project" and select "CODESYS Control Raspberry Pi SL" as the device.
• Define the target system by means of the Network scan.

• Insert a "BACnet Server" and a "BACnet Analog Value" object in the device tree:

• Every device in a BACnet network must have a unique ID. Set this in the tab BACnet Interface Parameters of the "BACnet Server" object.
  
  

Within a device, every instance of a BACnet object type (BACnet Analog Value, BACnet Binary Value, etc.) receives a unique ID. This remains unchanged here as the value "1".

• Adapt the "PLC_PRG" as follows:

VAR
    xSwitch        :    BOOL;
    lrValue        :    LREAL := 0.23;
END_VAR

// Numeric simulation
IF xSwitch then
    lrValue := lrValue + 0.01;
    IF lrValue >= 5.0 THEN
        xSwitch := False;
    END_IF
ELSE
    lrValue := lrValue - 0.01;
    IF lrValue <= -5.0 THEN
        xSwitch := True;
    END_IF
END_IF


BACnet_Analog_Value.PresentValue := lrValue;

Requirements for the BACnet client (As of BACnet-Version 1.2.0.0)

• Create a "Standard project" and select "CODESYS Control Win V3" as the device.
• Define the target system by means of the network scan (see BACnet server).
• Insert a "BACnet Server" object and rename it to "BACnet_Client"
  
  
  
  
  

• Adapt the "PLC_PRG" POU as follows:
  
  

  ---

  Declaration

  VAR

  fbReadProperty : BACnet.BACnetClientReadProperty;
  xReadExecute : BOOL;
  lrReadValue : LREAL;
  xInitDone : BOOL := FALSE;
  END_VAR

  ---

  Declaration

  VAR
  	fbReadProperty	: BACnet.BACnetClientReadProperty;
  	xReadExecute	: BOOL;
      lrReadValue		: LREAL;
  	
  	xInitDone 		: BOOL := FALSE;
  END_VAR

  ---

  Implementation

  IF NOT xInitDone THEN
  	fbReadProperty.RegisterToServer(BACnet_Client);
  	fbReadProperty(dwTargetDeviceNumber := 718,
      				objType := BACnet.CmpBACnet.IEC_BACNET_OBJECT_TYPE.OBJ_ANALOG_VALUE, objInst := 1,
      				propID := BACnet.CmpBACnet.IEC_BACNET_PROPERTY_ID.PROP_PRESENT_VALUE);
  	xInitDone := TRUE;
  ELSE
  	fbReadProperty(xExecute := xReadExecute);
  	IF fbReadProperty.xDone THEN
  		xReadExecute := FALSE;
  		lrReadValue := BACnet.GetRealFromContents(fbReadProperty.result);
  	END_IF
  END_IF

  ---

Requirements for the BACnet client (Up to BACnet-Version 1.2.0.0)

• Create a "Standard project" and select "CODESYS Control Win V3" as the device.
• Define the target system by means of the network scan (see BACnet server).
• Insert a "BACnet Server" object and a "BACnet Client Property Access" object in the device tree.

• Adapt the "PLC_PRG" POU as follows:

VAR
    readPropertyFB     	: BACnet.ClientReadProperty;
    readReal         	: LREAL;
END_VAR

//Simply execute the FB reading out a property
readPropertyFB(clientFB := BACnet_Client_Property_Access,
                dwTargetDeviceNumber := 718,
                objType := BACnet.CmpBACnet.IEC_BACNET_OBJECT_TYPE.OBJ_ANALOG_VALUE,
                objInst := 1,
                propID := BACnet.CmpBACnet.IEC_BACNET_PROPERTY_ID.PROP_PRESENT_VALUE);
    
//Start execution and send BACnet-request to BACnet-network
IF NOT readPropertyFB.xExecute THEN
    readPropertyFB.xExecute := TRUE;
END_IF


//Wait for the answer on the request. When xDone is TRUE, an answer has been received.
IF readPropertyFB.xDone THEN
    //Read out the answers contents
    readReal := BACnet.GetRealFromContents(readPropertyFB.ReadPropertyResult);
    //Reset FB and also its contents
    readPropertyFB.xExecute := FALSE;
END_IF

Downloading and starting the projects

BACnet server

• Download the application to the PLC.

BACnet client

• Download the application to the PLC.

Reading a device property

If for example general properties of the device be read, then you have to pay attention that the ID of the device number agrees with the object instance.
Example: Reading the revision number of the firmware:

readPropertyFB(xExecute := xExecute,
                clientFB := BACnet_Client_Property_Access, 
                dwTargetDeviceNumber := 718,
                objType := BACnet.CmpBACnet.IEC_BACNET_OBJECT_TYPE.OBJ_DEVICE, 
                objInst := 718,
                propID := BACnet.CmpBACnet.IEC_BACNET_PROPERTY_ID.PROP_FIRMWARE_REVISION);