Deductive fault diagnosis in digital circuits: a survey

Fault diagnosis in digital circuits is normally based on prior computation of fault symptoms using explicit fault models and simulation followed by matching of the observed symptoms of a faulty circuit with one of the sets of precomputed symptoms. Some attempts have been made, however, at diagnosis without fault simulation by deducing the location of a fault or faults from the observed symptoms and from fault-free models of circuit behaviour only. The paper traces the early development of fault diagnosis techniques which avoided fault simulation, and then reviews the published literature on deductive techniques. Three main methods of deductive fault diagnosis are reviewed and all are shown to have limitations, some due to the use of the stuck-fault model and others due to the combinatoric problems associated with multiple faults and the resulting multiplicity of choices which an algorithm must pursue. The problem of test selection is discussed together with the choice, in future work, of processing the results of one test at a time and then combining the diagnoses from each test, as in two of the methods reviewed, or of processing a multiple set of tests together as in the other main method reviewed.