1 Introduction
Functional test sequences are applied to a sequential circuit in its functional mode of operation. A functional test sequence specifies the values to be applied to the primary inputs during test application. Unlike structural tests, functional test sequences avoid the use of scan chains. Functional test sequences may be used for manufacturing testing since they detect defects that are not detected by scan-based tests [1], or to avoid overtesting. Overtesting occurs when at-speed scan-based tests are used for detecting delay faults, and create nonfunctional operation conditions during functional capture cycles [2], [3]. Functional test sequences may also be used for speed binning. The study in [4] shows that circuits fail at significantly lower frequencies under scan-based tests than under functional test sequences that have similar delay fault coverage. Therefore, scan-based tests underestimate the circuit speed, and a more accurate estimate is obtained using functional test sequences.