The architecture and operation of an 1149.1-based digital bus monitor (DBM) IC is described. The ability of the DBM to monitor at-speed signal transfers between ICs in real time provides a method of monitoring the functional operation of circuits assembled on board and multichip module substrates. Such tests can be used to reveal timing sensitive and/or intermittent failures that would otherwise not be detectable without the use of external testers and mechanical probing fixtures. This test approach may, in some cases, reduce the cost to manufacture and support a product by reducing the need for test equipment in both factory and field environments.
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