To simulate tri-state logic in a non-pessimistic way, a six valued algebra is shown to be necessary. This is then extended to quin-state logic (strong 0, strong 1, weak 0, weak 1, high impedance) and a fifteen valued algebra. The improved accuracy is as important for fault simulation as for design verification. The requirements for non-pessimistic test generation algebras for tri-state and quin-state logic are also discussed. Pessimism in test generation increases the search space and hence the run time.
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