On Finding Don't Cares in Test Sequences for Sequential Circuits
Yoshinobu Higami, Seiji Kajihara, Irith Pomeranz, S. Kobayashi, Yuzo Takamatsu · IEICE Transactions on Information and Systems · 2006
Recently there are various requirements for LSI testing, such as test compaction, test compression, low power dissipation or increase of defect coverage. If test sequences contain lots of don't cares (Xs), then their flexibility can be used to meet the above requirements. In this paper, we propose methods for finding as many Xs as possible in test sequences for sequential circuits. Given a fully specified test sequence generated by a sequential ATPG, the proposed methods produce a test sequence containing Xs without losing stuck-at fault coverage of the original test sequence. The methods apply an approach based on fault simulation, and they introduce some heuristics for reducing the simulation effort. Experimental results for ISCAS'89 benchmark circuits show the effectiveness of the proposed methods.