Functional test and diagnosis: a proposed JTAG sample mode scan tester

The author describes a JTAG (Joint Test Action Group) sample mode scan tester for diagnosis of at-speed failures in modules. The sample mode scan tester prototype system is fully capable of sampling nodal test data using the JTAG boundary scan protocol. With an internally developed test module as a test case, applications have been developed that successfully sample the response data from the MUT (module under test) and trace MUT failures to the failing scan bit(s) in the scan chain. Initial results indicate that sample mode testing is a viable means of diagnosing module faults in cases in which lack of physical access prevents traditional functional test methods from being used. Using boundary scan latches at device boundaries and connecting these devices to bring the resulting scan chain to the module edge connector provide the internal observation points necessary for diagnosing functional test failures