| 摘要 |
<p>PURPOSE:To attain the application of an EEPROM by the frequency higher than its assured frequency by shifting the back-up data to an unused area when the writing frequency of the back-up data reaches the assured frequency of a P-ROM which can be electrically erased. CONSTITUTION:A P-ROM (EEPROM) 3 which can be electrically erased and has the capacity larger than the twice of the capacity of the back-up data is provided as a back-up memory. The back-up data is written into the EEPROM 3 and the counted writing frequency is compared with an assured frequency. Then the back-up data are all shifted to an unused area and copied there when the coincidence is obtained between both frequencies. In this case, the count value is cleared and the area number is rewritten. As a result, the EEPROM 3 can be used by the frequency higher than its assured frequency.</p> |
