RESET DEVICE FOR MICROCOMPUTER

摘要

PROBLEM TO BE SOLVED: To make the microcomputer start operating after securely being reset without changing the design for every application circuit of the microcomputer by switching the clock source of the microcomputer to an external clock when an adjusted divided voltage exceeds a reference voltage. SOLUTION: When the power source is started up, a selector 28 supplies an internal clock to a CPU 29. When the voltage division output proportional to the source voltage Vcc a reset circuit 12 rises above the reference voltage, a reset circuit 12 makes a RESET signal insignificant to reset the resetting of the CPU 29. The CPU 29 adjusts the voltage division output Vd2 by adjusting the resistance value of a variable resistance 20 of a voltage detecting circuit 18. The voltage detecting circuit 18 compares the voltage division output Vd2 with the reference voltage Vref and when the voltage division output Vd2 rises above the reference voltage Vref, the CPU 29 changes the position of the selector 28. The clock source of the CPU 29 is switched to the external clock.