| 摘要 |
PURPOSE:To prevent firmware from being used illegally without making an I/O circuit complicate by providing at least one CPU, a main memory part, an instruction ciphering decoder circuit and an instruction ciphering key circuit outputting instruction ciphering decoding signals. CONSTITUTION:For executing a program, the CPU 1 supplies an instruction fetch control signal regarding instructions inputted from the ROM 4 of the main memory part MM 2 to the instruction ciphering decoder circuit 5 through an instruction fetch control line 8 to set the circuit 5. An instruction ciphering key circuit control signal is supplied to the instruction ciphering key circuit 6 from the CPU 1 through a circuit control line 9 to set the circuit 6. Whenever instructions are inputted to the circuit 5, the circuit 6 supplies the instruction ciphering decoding signal through an instruction ciphering decoding circuit activation line 10. The circuit 5 decodes a ciphered program, and supplies it to the CPU 1 through a data bus 7. Then the CPU 1 executes the instruction. |
