Node-fault diagnosis and a design of testability

A concept of k-node-fault testability is introduced. A sufficient and almost necessary condition for testability as well as the test procedure is presented. This condition requires little computation with a few test points in view of the complexity of the problem of multifault diagnosis of large-scale circuits. This condition is further evolved to a necessary and almost sufficient condition for testability. A unique feature of this condition is that it depends only on the graph of the circuit, not on the element values. Based on this condition, a design of testability is established.