Logic Built-In Self-Test 265 for testing the functional circuitry at the system, board, or chip level to ensure product quality. Functional offline BIST performs a test based on the functional specification of the functional circuitry and often employs a functional or high-level fault model. Normally such a test is implemented as diagnostic software or firmware. Structural offline BIST performs a test based on the structure of the functional circuitry. There are two general classes of structural offline BIST techniques: (1) external BIST , in which test pattern generation and output response analysis is done by circuitry that is separate from the functional circuitry being tested, and (2) internal BIST , in which the functional storage elements are converted into test pattern generators and output response analyzers. Some external BIST schemes test sequential logic directly by applying test patterns at the inputs and analyzing the responses at its outputs. Such techniques are often used for board-level and system-
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