| 摘要 |
PURPOSE:To improve the secrecy of data by preventing the data stored in a memory from being illegally read out by writing a deciphering code in a register and further enabling a change. CONSTITUTION:The data ciphered in advance are stored in a ROM 1, and registers 8 and 9 are provided to set the deciphering code for converting those data to normal data. The deciphering code can be arbitrarily, set through an input gate 14 to these registers 8 and 9. When reading the data in the ROM 1, the logic with the deciphering code of the registers 8 and 9 is calculated by a logic circuit 16 and outputted from input/output terminals 2 and 3 through an output gate 15 which performs an operation inverted from an input gate 14. Thus, since the deciphering code is written in the registers 8 and 9, the deciphering code is not fixed into one but the deciphering code can be changed by reloading the values of the registers 8 and 9 as needed. Besides, the secrecy of data can be held for a manufacturing person as well. |
