| 摘要 |
PCT No. PCT/JP95/00429 Sec. 371 Date Sep. 11, 1997 Sec. 102(e) Date Sep. 11, 1997 PCT Filed Mar. 15, 1995 PCT Pub. No. WO96/28826 PCT Pub. Date Sep. 19, 1996In a memory device using an electrically rewritable nonvolatile memory as a storage medium, wherein, in order to allow the memory to deteriorate evenly, the erasing time and writing time are measured, the influence of scatter of cells in the memory being eliminated on the basis of the resultant measurement values, a substantial degree of deterioration being thereby determined with a high accuracy, whereby a memory device of a high reliability and a high efficiency is practically obtained. In order to rewrite an electrically rewritable nonvolatile memory (1), there are provided a means for measuring the erasing time and writing time, a means for comparing an erasing time with a stored reference time, a means for correcting writing time on the basis of the results of the comparison, and a means for determining deterioration on the basis of the results of the correction. According to the present invention, the substantial deterioration of each cell can be determined, and such control is possible that more deteriorated memory is used less frequently while less deteriorated memory is used more frequently. As a result, the reliability of the memory is improved, and the memory can have a longer service life.
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