Invalid REF= assignment
REF=
assignments are considered valid if the left-hand side of the assignment is a pointer variable
and the right-hand side is a variable of the type that is being referenced.
For example assignments such as the following are invalid
VAR
foo : DINT;
bar : DINT;
qux : SINT;
refFoo : REFERENCE TO DINT;
END_VAR
refFoo REF= 5; // `5` is not a variable
foo REF= bar; // `foo` is not a pointer
refFoo REF= qux; // `refFoo` and `qux` have different types, DINT vs SINT