Progress in PLC programming for distributed automation systems control

Industrial automation plants are controlled essentially by PLC-based control systems. PLCs are today mostly programmed in the languages of the IEC 61131-3 standard which are not ready to meet the new challenges of widely distributed automation systems. Currently, different solutions are under development from industry and research: an extension of IEC 61131-3 which includes object oriented programming; the adoption of the new standard IEC 61499 which makes the software execution event-based instead of scan-cycle based as in IEC 61131-3 standard. In this paper it is shown how object oriented programming implicitly makes event-based the PLC software behavior. Moreover, it is shown how supervisory control can help in designing correct software in this context.