Improving the Diagnostic Resolution of Built-In Test
Original Publication Date: 1988-Jan-01
Included in the Prior Art Database: 2005-Feb-14
This disclosure shows that in self-test, also known as built-in test, if a frame produces an error signature during test, the error signature may still be used. The error signature is used by computing a new expected signature at each frame. Built-in test uses an internal multi-input signature analyzer (MISR) to compress the responses of the circuit to the test patterns. At the end of the test the final MISR state, or the signature of the circuit, is unloaded and compared with the known correct signature. A mismatch indicates a faulty circuit and diagnosis to a repair action is required. The first diagnostic step is to identify the failing tests. The test sequence is subdivided into individual frames of, say, 256 tests each and the complete test sequence is repeated with a pause at the end of each frame.