A design verification method for programmable controller software

The conditions under which sequentialized logic in software exhibits undesirable behavior are explored and a design verification method is proposed. The method consists of two steps. (1) Input signals to the extracted section of the sequential control diagram including a feedback loop, which cause three kinds of potential states, (a) reset failure, (b) set failure, and (c) simple delay, are applied to the feedback loop in order to evaluate a failure possibility. (2) The input signals that cause a failure of the circuit output are identified using a simulation technique of backward signal propagation. Experiments with a simple sequential circuit confirms that this method can detect all the conditions which lead to undesirable behavior