Implicit state transition graphs: applications to sequential logic synthesis and test

Implicit state enumeration is used in developing strategies to solve key problems in sequential logic synthesis and test. It is shown that it is possible to extract implicit state transition graphs (ISTGs) from logic-gate and flip-flop descriptions of sequential circuits that allow equivalent states to be represented by cubes, and edges from different states to be coalesced into one, thereby decreasing significantly the CPU time and memory requirements of the extraction process. Coupled with the enumeration technique, synthesis strategies are proposed for FSMs (finite state machines) described at the logic level. As is illustrated, these synthesis strategies allow the authors to optimize large FSMs. The authors apply an ISTG traversal algorithm for verifying equivalence and detecting redundancies in logic-level sequential circuits. This algorithm is more efficient than previously developed sequential test generation algorithms when used to detect equivalent-state redundancies present in some classes of circuits.<>