Formal Verification of PLC Programs

This paper presents an approach to the verification of programs for programmable logic controllers (PLCs) using SMV, a software package for formal verification of state transition systems. Binary PLC programs are converted directly into SMV modules that retain the variable names and execution sequences of the original programs. The system being controlled is modeled by a C/E system block diagram which is also transformed into a set of SMV modules, retaining the structure of the block diagram model. SMV allows the engineer to verify the behavior of the control program over all possible operating conditions. Mechanisms are discussed for representing correctly the concurrent execution of the PLC programs and the plant model using SMV primitives. The SMV approach to PLC program verification is illustrated with an example.