Semantic Warning (SEM2010): The external usage of VAR_IN_OUT parameters is not allowed. No code will be generated for this statement.
Formal parameters of a function block which are declared with the 'Usage = InOut' must not be used in a direct way outside of the FB.
Reason: The direct external usage of an FB in/output formal parameter could result in an undefined parameter value if the FB is not executed before reading the parameter. This may result in an unstable controller application. Therefore, no code is generated for the statement.
Correct usage: instead, the in/output parameter must be assigned to a variable in the context of a regular FB call. This variable can then be used as it contains the same value.
Example: the Boolean in-output formal parameter state of the MyFB function block cannot be used as control variable in an IF statement of a calling program POU MySTprogram. Instead, state is assigned to the local variable FBStatus in the context of the MyFB1 instance and then FBStatus is used in the IF statement.
This is a warning message to inform you about that important issue. Check the reason for this warning. If it is intended, no corrections are required as reaction to this message.