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Unformatted text preview: of an unreachable state. Likewise, if a justification sequence has been successfully computed for state S before, and a different target fault requires the same state S , the previous justification sequence can be used to guide the search. Note that, because the target faults are different, the justification sequence may not simply be copied from the solution for one fault to another. 4.5.3 Gated Clocks and Multiple Clocks All the algorithms for sequential ATPG thus far assumed the sequential circuit has a single global clock. This assumption is simple as all memory elements (flip-flops) switch synchronously at every clock; however, in modern digital systems, this assumption is often not true. For instance, gated clocks (illustrated in Figure 4.32a) and multiple clocks (Figure 4.32b) are becoming mainstream. Gated clocks are...
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- Spring '08