| 摘要 |
PROBLEM TO BE SOLVED: To prevent the execution of a mal-correction based on past data during an external code correction by incrementing the pass number stored in each synchronous block and discriminating written data to determine whether the data are present or the one in the past using the pass number. SOLUTION: A comparative collating of a pass number is conducted and the data having no expected pass number are assumed to be the data whose errors are not compensated for during an internal code correction. Then, discrimination is made to determine whether the data in a SDRAM (a synchronous block) are updated or not employing the pass number. Note that the data, which are not updated, are treated as error data. Moreover, if normal data, which have no error due to an internal code correction, exist for 1/2 of a parity number, i.e., less than the number of a normal correction limit, an external code correction by the normal correction is inhibited. Thus, the execution of a mal-correction by an external code correction mainly using the unupdated past data is prevented.
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