Fault simulation for synchronous sequential circuits is a very time-consuming task. The complexity of the task increases if there is no information about the initial state of the circuit. In this case an unknown initial state is assumed which is usually handled by introducing a three-valued logic. As it is well-known fault simulation based on this logic only determines a lower bound of the fault coverage. Recently it has been shown that fault simulation based on the multiple observation time test strategy can improve the accuracy of the fault coverage. In this paper we describe how this strategy can be successfully implemented based on Ordered Binary Decision Diagrams. Our experiments demonstrate the efficiency of the fault simulation procedure developed.
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