Selection of Primary Output Vectors to Observe Under Multicycle Tests
Irith Pomeranz · IEEE Transactions on Very Large Scale Integration (VLSI) Systems · 2019
Test compaction benefits from the use of multicycle tests that have several clock cycles between their scan-in and scan-out operations. For maximum benefit, primary output vectors should be observed during all the clock cycles between the scan operations of a multicycle test. This allows the test to detect all the faults whose fault effects reach the primary outputs, in addition to the ones whose fault effects are latched onto the flip-flops before the scan-out operation. However, for consistency with single-cycle tests for single stuck-at faults, or two-cycle tests for transition faults, only one primary output vector should be observed per test. This can be the last primary output vector of the test, as in the case of single-cycle and two-cycle tests, but other options are more useful, as demonstrated in this article. In particular, this article suggests that the primary output vector to be observed should be selected individually for every test. It also describes a static procedure for selecting a single primary output vector to observe individually for every test based on a given compact multicycle test set and a dynamic test compaction procedure that produces multicycle test sets with this property.