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

Abstract

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.