Exceptions Handling in Hierarchical Petri Net Based Specification for Logic Controllers

Hierarchical Petri nets beside UML state machine diagrams, sequentional function charts (SFC) and hierarchical concurrent state machines are common solution for specification of logic controllers. These specification formats provide both concurrency and modeling on multi levels of abstraction (hierarchic approach). But only state machine diagrams supports exceptions handling in direct way. Program model presented in form of state machine diagram may be later transformed into a program in the SFC language or transformed in the Petri Net and implemented in the FPGA structure. Similarity between SFC language and Petri Nets give us lot of tools for analysis such control system[3]. Article presents new approach for exceptions handling in hierarchical Petri nets as formal specification for logic controllers. Proposed method of specification can be used independently or as a part of dual specification (correlated state machine diagram and hierarchical Petri Net).