| 摘要 |
PURPOSE:To prevent the secrecy of data in a ROM from leaking by providing a switching circuit which converts an address signal outputted from a CPU and outputting the conversion result to an address decoder at the time of a program memory test. CONSTITUTION:A switching circuit 9 is provide which outputs the address signal 6 from the CPU1 to the address decoder 5 as a signal 10 without conversion in normal operation with a control signal I, but converts the address signal 6 from the CPU1 into a signal 10 and outputs the signal 10, to the address decoder 5 at the time of a ROM test. Then data in an address of the ROM2 corresponding to the value of an input bit is outputted in the normal operation, but when a ROM read is tested, data in an address corresponding to the converted value of the input bit is read out. Consequently, the 3rd party hardly reads the ROM2 in ROM read test mode and the secrecy of data in the ROM2 is kept. |
