Static slicing for PLC program with ladder transformation

PLC (programmable logic controller) is one type of general industrial control platforms with high reliability, which has been widely used in many real-time control systems, such as transfer lines and continuous casting machines. With the increasing size and complexity of PLC programs, the traditional manual test cannot meet the needs of industrial fields due to its inefficiency and error-prone features. Program slicing is a method of program analysis and understanding. Based on some slicing criterion, it removes the irrelevant statements from the source code to obtain a group of interested program segments. In this way, the scope of the program under study is narrowed. In this paper, program slicing of PLC programs will be studied. The slicing of PLC programs needs special treatment which is usually not necessary in other software written in high level language or assembly language. For example, PLC programs run in cyclic operating mode, and they usually allow each ladder to include more than one output ports making the number of outputs in one statement much larger than that of those in other software. We first introduce a ladder transformation as a preparation for program slicing. Then algorithms for static slicing for PLC programs are proposed. A demo is given to show that this method can effectively reduce the scale of program.