JPS6468668A - Data compressor - Google Patents

Abstract

PURPOSE:To reduce a fault overlook rate by composing the data compressor of a linear feedback shift register whose feedback position can be selected in plural ways. CONSTITUTION:When a selection control signal SC is held at high level, an exclusive OR circuit EXOR2 ORs the output signals of data latch circuits DL3 and DL4 and the linear feedback shift register LFSR employs a generating polynomial which has the output terminals of the circuits DL3 and DL4 as feedback positions. When the signal SC is lowered to low level, a polynomial which has the output terminals of the DLs 2 and 4 as feedback positions is employed. Then when test input data Din is supplied to the LFSR, the data is shifted cyclically for the current generating polynomial, and compressed into four bits and held. Thus, Din is supplied to the LFSR repeatedly under the different generating polynomials and the fault overlook rate obtained by the (m)-stage LFSR is reduced to 1/2<2m>.