Abstract: This paper presents a new test data compression/decompression method for SoC testing,called hybrid run length codes.The method makes a full analysis of the factors which influence test parameters:compression ratio,test application time,and area overhead.To improve the compression ratio,the new method is based on variable-to-variable run length codes,and a novel algorithm is proposed to reorder the test vectors and fill the unspecified bits in the pre-processing step.With a novel on-chip decoder,low test application time and low area overhead are obtained by hybrid run length codes.Finally,an experimental comparison on ISCAS 89 benchmark circuits validates the proposed method.

Key words: test data compression, unspecified bits assignment, system-on-a-chip test, hybrid run-length codes