MODELING DIGITAL CIRCUITS FOR TROUBLESHOOTING

Existing methods for model-based troubleshooting have not previously scaled up to deal with complex digital circuits, in part because traditional circuit models do not represent aspects of the device that troubleshooters consider important. An instruction level simulation of a microprocessor explicitly represents the logic levels present on its external bus at every clock edge, but not the fact that during normal operation those bus signals should be very active. A schematic may represent the connectivity of field replaceable components, but does not show how their combined behavior implements the intentions of the designer. The specifications of a component rarely say how it is likely to fail. This suggests basing troubleshooting on a specialized circuit model that emphasizes such aspects. Although it is beyond current technology to derive such models from circuit schematics automatically, this work shows that these models can make the troubleshooting of complex circuits feasible. This paper describes an implemented program for troubleshooting complex digital circuits, using a representation that makes explicit their behavior at a high level of temporal abstraction, their physical and functional organization, and the common ways that their components fail.