LAUSR

Functionally possible scan-based tests create functional operation conditions during their functional capture cycles. This is important for avoiding failures that are caused by nonfunctional operation conditions rather than faults. However, the fault coverage achievable by functionally possible scan-based tests is lower than that achieved by unconstrained scan-based tests. In addition, the tests are fully specified, limiting the applicability of both test compaction and test data compression. This article introduces an approach, where a multicycle functionally possible scan-based test set is obtained from a compressed test set $S$ as a dual of the unconstrained multicycle scan-based test set that $S$ produces. A dual functionally possible scan-based test is obtained by replacing the scan-in state of an unconstrained test with the all-zero state (or the initial state of the circuit for functional operation). The procedure described in this article modifies a given compressed multicycle test set to improve the fault coverage achieved by the dual functionally possible scan-based test set. Experimental results for benchmark circuits demonstrate the effectiveness of this approach.