PROPERTIES OF FAULTS IN SYNCHRONOUS SEQUENTIAL CIRCUITS AND THEIR APPLICATION TO TEST GENERATION, LOGIC OPTIMIZATION, AND TESTABLE DESIGN

Abstract

We consider properties of faults in synchronous sequential circuits that facilitate test generation and obtaining fully testable circuits. Most practical circuits have synchronizing sequences. Synchronizing sequences are important in facilitating the test generation process for detectable faults, and in identifying undetectable faults. Synchronizing sequences are also important in determining whether an undetectable fault can be removed from a circuit without affecting its normal operation, i.e., in determining whether a fault is "redundant".

We describe several results related to synchronizable circuits and their synchronizing sequences. We show a class of faults for which a synchronizing sequence for the faulty circuit can be determined at very low simulation cost from the synchronizing sequence of the fault free circuit. New methods to determine undetectable and redundant faults, and to remove logic associated with redundant faults are presented. Experimental results are presented to demonstrate the effectiveness of the proposed methods.

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