Combinational testing of PLC programs based on the denotational semantics of instructions

The correctness of PLC (Programmable Logic Controller) program in automatic control is vital to this kind of safety-critical applications. In this paper, we present a useful method of combinational testing for correctness of PLC programs. The method is based on the denotational semantics of PLC program and the semantic functions for basic instructions. It establishes the definition of denotational semantics for PLC program. The function of denotational semantics is defined by extended λ-calculus. It analyses adaptive problems of various tests for PLC embedded software and proposes a combinational testing framework based on simulation mechanism. The equivalent transforming module of PLC program is defined by means of test module composed with high-level language code segments, which have equivalent denotational semantics and partly include program diagnostic information. The framework can decompose a PLC program test into some small tests, and solve the test problem under the condition of boundary and utmost or no environment supporting. The validity of our method is shown by one example of experiments.