In this paper, a novel mixed selection methodology using flip-flops for scan and reset design is proposed. The method runs test generation for a sequential circuit to obtain reachable states of flip-flops and required states for hard-to-detect faults. The circuit is also explored so as to acquire the structural connection relationship among the flip-flops. By analyzing these three sets of information, the flip-flops can be arranged in an appropriate order for mixed partial scan and reset selection. Instead of selecting the best flip-flop to revise the circuit for the next test generation, we give first priority to independent flip-flops each time in order to reduce the number of iterations. Experimental results show that this method can achieve higher testability with fewer scan/reset flip-flops than can either the scan only or the previous mixed scan/reset methods.

Keywords: partial scan, partial reset, reachable states, test generation, design for testability

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Received June 30, 1999; revised December 23, 1999; accepted March 7, 2000.
Communicated by Kuen-Jong Lee.
^*This work was supported in part by the National Science Council, Taiwan, R.O.C. under Grant NSC-88-2215-E238-002.