Symbolic Simulation Based Techniques for Debugging Discrete Control Programs

Abstract Symbolic Simulation-Based Debugger (SSBD) is a new tool for debugging discrete control programs interactively. Given the control program and a partial model of the plant, SSBD finds the set of all possible causes for an observed transient behavior using symbolic simulation. The SSBD procedure is described in detail for a Boolean representation of relay ladder logic (RLL). A more general graph-based data and control flow representation of discrete control programs is introduced as to enable analysis of control programs using difficult-to-analyze features such as conditional jumps, looping, and temporary variables.