| 摘要 |
PURPOSE:To keep the contents of a program completely secret to the 3rd person without spoiling the function of checking the contents of the program by providing a means which makes an input signal inputted by external operation invalid forcibly. CONSTITUTION:The input signal I2 of an FETQ7 is held at a low level at a debugging request and an output terminal (0) is held at a high level to output a control signal to an EPROM program memory part 2, obtaining circuit constitution which debugs the contents of the program memory. When the need to control the program memory externally is eliminated after the debugging, an input signal I1 is held at the low level and a high voltage is impressed to a power source VDD at the same time. Then, a minus charge is stored in the floating gate of an EPROM cell Q4 to inhibit a memory control function. This state is reset by returning the cell Q4 to its original state by ultraviolet ray irradiation, etc., but the data in the memory are erased completely by the irradiation and the secrecy is held completely. |
