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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 0controllability of
s
±
CC1(
s
)—combinational 1controllability of
s
±
CO(
s
)—combinational observability of
s
±
SC0(
s
)—sequential 0controllability of
s
±
SC1(
s
)—sequential 1controllability 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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 Spring '08
 elbarki

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