76_pdfsam_VLSI TEST PRINCIPLES & ARCHITECTURES

76_pdfsam_VLSI TEST PRINCIPLES & ARCHITECTURES -...

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Design for Testability 45 To observe an input of the AND gate at d requires setting the other input to 1; therefore, the combinational and sequential observability measures for both inputs a and b are: CO ±a² = CO ±d² + CC1 ±b² + 1 SO ±a² = SO ±d² + SC1 ±b² CO ±b² = CO ±d² + CC1 ±a² + 1 SO ±b² = SO ±d² + SC1 ±a² It is important to note that controllability and observability measures calculated using SCOAP are heuristics and only approximate the actual testability of a logic circuit. When scan design is used, testability analysis can assume that all scan cells are directly controllable and observable. It was also shown in [Agrawal 1982] that SCOAP may overestimate testability measures for circuits containing many reconvergent fanouts; however, by being able to perform testability analysis in O ( n ) computational complexity for n signals in a circuit, SCOAP provides a quick estimate of the circuit’s testability that can be used to guide testability enhancement and test generation.
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This note was uploaded on 05/16/2011 for the course ENGINEERIN mp108 taught by Professor Elbarki during the Spring '08 term at Alexandria University.

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