LFSR-Based Generation of Multicycle Tests

This paper describes a procedure for computing a multicycle test set whose scan-in states are compressed into seeds for a linearfeedback shift register, and whose primary input vectors are held constant during the application of a multicycle test. The goal of computing multicycle tests is to provide test compaction that reduces both the test application time and the test data volume. To avoid sequential test generation, the procedure uses a single-cycle test set to guide the computation of multicycle tests. The procedure optimizes every multicycle test, and increases the number of faults it detects, by adjusting its seed, primary input vector, and number of functional clock cycles. Optimizing the seed instead of the scan-in state avoids the computation of scan-in states for which seeds do not exist. Experimental results for benchmark circuits are presented to demonstrate the effectiveness of the procedure.