266 VLSI Test Principles and Architectures CUT, and ORA be initialized to known states prior to self-test, and no unknown (X) values be allowed to propagate from the CUT to the ORA. In other words, the CUT must comply with additional BIST-specific design rules . There are a number of advantages to using the structural offline BIST technique rather than conventional scan: ± BIST can be made to effectively test and report the existence of errors on the board or system and provide diagnostic information as required; it is always available to run the test and does not require the presence of an external tester. ± Because BIST implements most of the tester functions on-chip, the origin of errors can be easily traced back to the chip; some defects are detected without being modeled by software. N-detect , a method for detecting a fault N times, is done automatically. At-speed testing, which is inherent in BIST, can be used to detect many delay faults. ± Test costs are reduced due to reduced test time, tester memory requirements,
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