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Redundancy Identification Using Transitive Closure
 in Proc. of the 5th Asian Test Symp
, 1996
"... We analyze all signals of a combinational circuit simultaneously for redundancy. The state of a signal is represented by two binary variables. The first variable is the logic value of the signal. The second variable is the observability status of the signal with respect to all primary outputs. Boole ..."
Abstract

Cited by 11 (5 self)
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We analyze all signals of a combinational circuit simultaneously for redundancy. The state of a signal is represented by two binary variables. The first variable is the logic value of the signal. The second variable is the observability status of the signal with respect to all primary outputs. Boolean equations specify local relationships of these variables in a manner similar to the neural network or Boolean satisfiability method. All pairwise terms appearing in these Boolean equations are used to construct an implication graph, for which the transitive closure graph is obtained. Any signal assignments or relations found from the transitive closure are substituted into higherorder terms of the Boolean equations, some of which reduce to pairwise terms. Such cases are iteratively included in the transitive closure until no more reductions are possible. In the final transitive closure, all signals are examined for the following conditions of redundancy: (1) If a signal and its complement imply each other (contradiction) then both stuckat faults on that signal are redundant; (2) If one value implies the other value (fixation) then one of the stuckat faults on that signal is redundant; (3) If the true observability status of a signal implies its own false observability status, then both stuckat faults of that signal are redundant; (4) If a certain value of a signal implies the false observability status, then the corresponding stuckat fault is redundant. Despite the apparent similarities with the transitive closure based ATPG, the present method is quite different. Here transitive closure is computed just once, and not recomputed or updated separately for each fault as required in ATPG. We give ISCAS '85 benchmark results. For c6288, we could identify 31 out of 33 redu...