Major Description
It seems that all implementations of PlcValue seem to have an implementation of all "is" methods to simply return "true", actually they should check if the value is in the bounds of the given type.
For PlcByte, this might be correct, cause the value of a PlcByte can be stored in any of the larger types, but for a PlcInteger the "isByte" check should check the value of the integer values against the bounds of a Short type.