| 摘要 |
PURPOSE:To prevent erroneous write to a memory caused by a noise of a power source by a simple circuit by inhibiting write to the memory for a prescribed time, when the noise has been generated at the time of turning ON/OFF of the power source. CONSTITUTION:When a normal power source VCC (a) and a backup power source VBC (b) are inputted to a power source OR circuit 1 and the VCC becomes lower than (VBC-R) volts in a voltage comparator 2, a comparison result pulse of a low level is outputted. When a variation point of High Low or Low High of the comparison result pulse is detected, a pulse generator 3 outputs a variation point detecting pulse of Low of width of msec. Subsequently, a memory write protecting circuit inhibits a write control signal (g), when the variation point detecting pulse is Low, and outputs the control signal (g) as it is to a terminal (e), when the variation point detecting pulse is High. In such a way, erroneous write to a memory caused by a noise at the time of ON/OFF of the power source VCC is prevented. |
