| 摘要 |
PROBLEM TO BE SOLVED: To exclude the unauthorized use, reference and alteration of data stored in the inside by inputting masks of different logical levels to a first AND circuit which inputs a write request signal or a second AND circuit which inputs a readout request signal corresponding to the authenticated result of a password code. SOLUTION: The write request signal Wr from an external system and a write mask signal Wm from a mask control circuit 1 are inputted to the first AND(logical product) circuit 5, and the readout request signal Rr from the external system and a readout mask signal Rm from the mask control circuit 1 are inputted to the second AND circuit 6. Both the write mask signal Wm and the readout mask signal Rm go to logic O('0') when a mask is set, and go to 1('1') when it is released. Only when the mask is released, namely, the correct authenticated result of the password code is obtained, a memory write signal We and a memory readout signal Re are validated, which permits the access of a memory circuit 3 from the external system. |
