| 摘要 |
PURPOSE:To improve the reliability of a main storage device (MS) and an alternative memory function by checking the alternative memory function while substituting the MS with an alternative memory. CONSTITUTION:A 1-bit register 9 which holds the contents of data transmitted from a write register 5 to a memory chip 1 is arranged in parallel to a memory chip 1. Then when the contents of data read out of the MS are corrected and written in the alternative memory, the contents of its one bit are held in the register 9 and the address register 3a of the alternative memory side is not updated in a cycle wherein the address register 3b of the MS side is updated to read a next bit; and the written data is read out as it is and compared by a comparing circuit 10 with the contents held in the register 9 and when they coincide with each other,it is judged that the alternative memory function is in normal operation. The contents of the address register 3a are equalized to the contents of the address register 3b and the writing, reading, and comparison of the next bit are repeated. If the comparison result indicates dissident, the abnormality of the alternative memory function is reported to a CPU to interrupt the substitution of the alternative memory.
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