Diagnosis of multiple faults in combinational digital circuits by modelling of transition propagation along critical paths

Previously published approaches to fault diagnosis in digital circuits rely almost exclusively on cause-effect reasoning. Such methods fail in the case of multiple faults, faults not easily modelled and faults not included in the set for other reasons. In contrast, a few attempts have been made to develop fault diagnosis methods utilising effect-cause reasoning. In the paper a new method of this type, applicable to combinational digital circuits, is presented. The technique depends on the notion of a critical path. It is shown that analysis of applied test results using a model of the fault-free circuit can determine regions of the circuit which are operating correctly, and can also determine particular nodes to be stuck in the case of classical stuck-type faults. An Ada implementation of the technique is described and example diagnostic results are presented