72_pdfsam_VLSI TEST PRINCIPLES & ARCHITECTURES

72_pdfsam_VLSI TEST PRINCIPLES & ARCHITECTURES -...

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Design for Testability 41 2.2.1 SCOAP Testability Analysis The SCOAP testability analysis program [Goldstein 1979] [Goldstein 1980] calcu- lates six numerical values for each signal s in a logic circuit: ± CC0( s )—combinational 0-controllability of s ± CC1( s )—combinational 1-controllability of s ± CO( s )—combinational observability of s ± SC0( s )—sequential 0-controllability of s ± SC1( s )—sequential 1-controllability of s ± SO( s )—sequential observability of s Roughly speaking, the three combinational testability measures (CC0, CC1, and CO) are related to the number of signals that must be manipulated in order to control or observe s from primary inputs or at primary outputs, whereas the three sequential testability measures (SC0, SC1, and SO) are related to the number of clock cycles required to control or observe s from primary inputs or at primary outputs [Bushnell 2000]. The values of controllability measures range between 1 and infinite, while the values of observability measures range between 0 and infinite. As a boundary condition, the CC0 and CC1 values of a primary input are set to 1,
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