Formalization and Visualization of Non-binary PLC Programs

Programmable Logic Controllers (PLCs) have been of great eminence in manufacturing systems and will probably remain predominant for some time to come. To allow reimplementation on a new hardware and visualization of existing code, a formalization approach for PLC programs is proposed. The method presented here is not restricted to binary operations in the PLC code but also considers digital operations. In order to achieve compact visualization and efficient re-implementation an abstraction of the low level Instruction List (IL) programs is developed. The formalization of the abstracted code results in a compact finite state machine representation. The method is implemented using JAVA and XML technologies. The IL is converted to XML, the XML document object model (DOM) is used for parsing and scalable vector graphics (SVG) is employed to graphically represent the resulting automata. The presented approach is illustrated using STEP 5 IL from Siemens. The method is however generic, other IL dialects could be parsed if the corresponding description files are built.