There is no difference in the basic approach to generating automated diagnostics for analog, hybrid and digital subsystems using the Diagnostic Profiler and Diagnostician . In each case, the Diagnostic Profiler is used (1) to capture the design from a CAD generated EDIF or VHDL file, (2) to identify the faults covered by each test and (3) to generate the diagnostic knowledge base. At run-time, the pass/fail results of the tests are given to the Diagnostician and it uses the diagnostic knowledge base to interpret those results and provide, as appropriate, either the next best test or the faulty parts call-outs.

The advantages of this approach over manual techniques apply equally to analog, hybrid and digital subsystems. On the development and modification side, are the advantages of traceability, modularity, measurability and simplicity; on the run-time side, are quality and efficiency. It is almost impossible to exaggerate the Diagnostic Profiler and Diagnostician advantages over the typical hard-coded diagnostic logic found in traditional test programs with their dense tangle of IF-THEN or GO-TO statements that are traceable to the design and the tests' diagnostic significance only by the results they provide.

At run-time, the Diagnostician is more efficient than the guided probe technique often used in digital diagnostics. Unlike the guided probe technique, the Diagnostician considers the implications of each test result on all possible faults. As a result, it needs fewer measurements (probes) to isolate a fault. Furthermore, the Diagnostician can identify a test sequence in which each test will maximize the information useable for fault isolation. Use of this feature also reduces the number of measurements (probes) required for fault isolation, and therefore test time.

The digital test area differs from the analog area in the number of measurements (test steps) and in the availability of fault simulation tools. It also differs in the flow of symptoms from faults to measurement points. In the analog case, a fault symptom seen on the input of an active part will almost always be seen on its output. In the digital case, fault symptoms from two inputs can cancel each other out for specific test steps.

Because of the availability of fault simulation tools, development of digital tests and digital diagnostics follows a different development process from that used for analog tests and diagnostics. This process is as follows:

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Last modified: July 05, 2000