| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a semiconductor memory of multivalued storage which can shorten a time required for writing. SOLUTION: In a semiconductor memory of multivalued storage provided with a memory cell storing four values of '1-4' with difference of threshold values, when a logic level of low is inputted in a first writing operation, a memory cell is made a state '1', when a logic level of high is inputted, a memory cell is made a state '2', when a logic level of low is inputted in a second writing operation, a memory cell being a state '1' as a result of the first writing is kept a state '1' as it is, when a logic level of high is inputted, the memory cell is made a state '3', when a logic level of low is inputted in the second writing operation, a memory cell being a state '2' as a result of the first writing is kept a state '2' as it is, when a logic level of high is inputted, the memory cell is made a state '4'.</p> |
