Instance Variables - VAR_INST

TwinCAT does not store a VAR_INST variable of a method on the method stack like VAR variables, but on the stack of the function block instance. This means that the instance variable behaves like other variables of the function block instance and is not reinitialized each time the method is called.

Instance variables are only allowed in methods of a function block and you can only access such a variable within the method. You can monitor the variable values of instance variables in the declaration part of the method.

An instance variable can only be initialized with the value of another variable if this variable is accessible from the function block. Initialization with other instance variables or with input variables of the method is therefore not possible and leads to a compilation error.

Instance variables cannot be extended with an attribute keyword.

Sample:

METHOD MethLast : INT
VAR_INPUT
    nVar  : INT;
END_VAR
VAR_INST
    nLast : INT := 0;
END_VAR

MethLast := nLast;
nLast    := nVar;

See also:

• Object Method