Improving the Diagnosability of Digital Circuits

Testing and fault-diagnosis of core-based systems are both difficult problems. Being able to identify which module in the core-based system is faulty has become very important. In this paper, we present algorithms to introduce test points for improving the diagnosability of a digital system. We define a measure of diagnosability known as module resolution which relates to the number of circuit modules that are suspected to be faulty after the diagnostic test procedure has been completed. We present a technique to partition the system into subsystems such that they can be tested in isolation. We also concurrently arrive at a test schedule which minimizes the overall effort in diagnostic testing. We have developed a tool called DEBIT for identifying the number, type, and location of test points in the circuit. We report the results of applying the tool on several benchmark circuits. situations when a fault class cannot be mapped to a module and, as a result, there is ambiguity about the module(s) which is (are) faulty. Camurati et al. [2] proposed two diagnostic measures for digital circuits, diagnostic resolution (DR) and diagnostic power (DP). For a test set T and a fault set F, these are defined as