| 摘要 |
PURPOSE:To prevent output prohibited data at a prescribed address from being decoded by constituting an address decoder with a hardware, a comparing data read out from the address with the data stored in a serial I/O register, and prohibiting the output of the data to the outside when both data coincide with each other. CONSTITUTION:Assuming that the output of the content of an address is prohibited, it is comprised in the address decoder 1701. When a microprocessor inputs a result in which a personal identification number inputted from, for example, the keyboard of an external device, etc., is compared with the readout data of the address, etc., to the serial I/O register 163, noncoincidence in all the bias of XNOR circuits 1704, 1704... occurs. On the contrary to this, since the coincidence of two input of the XNOR circuits 1704, 1704... can be obtained when the personal identification number itself is stored in the serial I/O register 163 by the certain arithmetic processing of the microcomputer, the output of an AND circuit 1705 goes to high level, and the output is prohibited. In such a manner, it becomes hard to decode the data whose output is prohibited to the outside essentially. |
