Theory and practice of sequential machine testing and testability

Undetectable and redundant faults in synchronous sequential circuits have recently received wide attention. Previous classifications of detectable, undetectable and redundant faults in such circuits assume certain restrictions regarding the operation of the circuit-under-test. In this work, no restrictions are imposed, and faults are classified on the basis of the existence (or lack) of an input/output experiment that distinguishes the fault free and faulty circuits. It is shown that faults that were previously considered redundant are detectable according to the new definitions (detectable in a probabilistic sense). The practical usefulness of the fault classification presented is discussed.