Function Block Definition

The fbValue variable is an instance of the function block FB_Value which implements the I_Value interface. This function block will be used to demonstrate remote procedure calls (RPC) and property access through ADS.

The function block FB_Value includes:

• An RPC method called Sum that calculates the sum of two LREAL inputs and returns both the sum and a descriptive string message.

• A property called Value that can be accessed and modified remotely. This property uses the {attribute 'monitoring' := 'call'} pragma to allow read and write operations over ADS.

  Note: This feature isn’t supported on Windows CE-based devices.

Below is the full implementation of FB_Value:

FUNCTION_BLOCK FB_Value IMPLEMENTS I_Value
VAR
   _fValue : LREAL;
END_VAR

{attribute 'TcRpcEnable'}
METHOD Sum : LREAL
VAR_INPUT
    fA, fB : LREAL;
END_VAR
VAR_OUTPUT
    sMessage : STRING;
END_VAR
    Sum := fA + fB;
    sMessage := 
        CONCAT('The sum of ', 
        CONCAT(TO_STRING(fA),
        CONCAT(' and ', 
        CONCAT(TO_STRING(fB), 
        CONCAT(' is ', TO_STRING(Sum)
    )))));
END_METHOD

{attribute 'monitoring' := 'call'}
PROPERTY Value : LREAL
GET
    Value := THIS^._fValue;
SET
    THIS^._fValue := Value * 2;
END_PROPERTY

END_FUNCTION_BLOCK

• Method: Sum: This RPC-enabled method takes two LREAL parameters (fA and fB) as inputs and returns their sum. The output sMessage provides a summary of the calculation in text format, giving both the input values and the result.
• Property: Value: This property provides controlled access to the internal _fValue variable. In the GET accessor, it simply returns the current _fValue. In the SET accessor, it doubles the input value before storing it back into _fValue.