| 摘要 |
PURPOSE:To protect the secrecy of a program by attaining a constitution where a coincidence detecting circuit outputs a grant signal when the coincidence is secured between the ROM codes and the external input codes by an amount equal to the number of bytes set previously. CONSTITUTION:A coincidence detecting circuit 6 compares the codes equivalent to three bytes and outputs an overflow signal only when the coincidence is secure among all codes. Then the circuit 6 is set in a test mode when the logic level of a test terminal 3 is set high. When the terminal 3 is set at a high level, the addresses of a ROM 1 are successively inputted to the circuit 6 at and after an address O. At the same time, the codes equal to the ROM codes equivalent to three bytes are successively inputted via an external input port 5 synchronously with input of the ROM codes. Thus the overflow signal given from the circuit 6 is inputted to a control circuit 2, and the ROM codes are outputted to an external output port 4 at and after the 4th code in a ROM code output state. |
