In the combinational decompressors, the i bits are expanded with the help of a combinational circuit network into a higher number ( n> i) scan chain inputs. The decompressor may be either combinational or sequential. The code has r specified bits if each r-tuple of bits within the n-bit pattern can be set to an arbitrary value with the help of at most i information bits. Then we can characterize the expansion code by the number of specified bits r. Let us suppose that the number of bits in the expanded pattern is equal to n. The bits transferred from a tester to CUT can be considered to be free-variables as they can be set to an arbitrary logical value. Test patterns generated in an Automatic Test Pattern Generator (ATPG) are encoded, stored in a tester, transferred from a tester to the CUT, decompressed in the decompressor, and loaded into parallel CUT scan chains. The code parameters are chosen in such a way that the code guarantees the lossless transmission of a maximum number of care bits within the transmitted test pattern. Loosely compression codes are used for test data transfer from a tester to circuits under test (CUT). We quantify the benefits and costs of such nonlinear decompressors and verify the benchmark circuit test pattern encoding efficiency. In this paper, we propose a relatively fast heuristics that can be used for finding the decompressor nonlinear function truth tables guaranteeing a required number of specified bits within a test pattern. The decompressors placed on a circuit under test transform nonlinear binary code words into test patterns with the help of nonlinear combinational or sequential circuits. It causes better encoding parameters that can be found for the transformation of code words into a test pattern that can feed a circuit under test with a higher number of parallel scan chains. The key important characteristic of the nonlinear codes is that the maximum number of codeword bits may be higher than it is obtained for the linear code words while the number of individually specified bits is preserved. It was found that nonlinear binary codes could be used for encoding test patterns in a similar way as it is done using linear codes, and the compression efficiency may be higher. All trademarks, brands, and names are the property of their respective owners.Test patterns are usually transferred from the tester to the circuit under test in a compressed form as it minimizes test access mechanism bandwidth and transfer time. The term lzop is a shorthand for "the Lempel-Ziv-Oberhumer Packer" and holds no connection with potential owners of registered trademarks or other rights.
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