| 摘要 |
PURPOSE:To prevent the destruction of a memory content or the erroneous write from occurring, by providing a memory write permission accepting register which accepts and stores a memory write permission signal in addition to a lock register which stores a bit of memory lock information in a main memory device. CONSTITUTION:A write permission register 5 is set before a write operation, and a write permission accepting register 11 in the main memory device 6 is set by the signal. At this time, by selecting a protection block by the lock register 7 based on the address information of a first memory address register 2 sent from a controller 1, a bit of memory lock information (11) of 0-1k words is outputted. Since the bit of memory key information (11) of a key register 3 sent from the controller 1 coincides with the bit of memory lock information (11), a matching condition is satisfied in this case, then, the output signal of a matching circuit 8 is outputted to an AND gate 12. The write permission signal of a write permission accepting register 13 is supplied, and a data is written.
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