Test Generation 233 is done because the intermediate state of the scan cells may cause contention in some of the signals in the logic, as well as reducing the power consumption in the combinational logic during the shifting of the data in scan cells. In addition, hold-scan cells also help increase the diagnostic capability on failing chips in which the data captured in the scan chain can be retrieved. In terms of test data volume, enhanced-scan tests may actually require less storage to achieve the same delay fault coverage. In other words, for launch-on-capture or launch-on-shift to achieve the same level of fault coverage, many more patterns may have to be applied. Unlike stuck-at faults, where a fault is either detected or not detected by a given test vector, a path-delay fault may be detected by different test patterns (consisting of two vectors) with differing levels of quality. In other words, some test patterns can detect a path-delay fault only with certain restrictions in place. Higher quality
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