The internal clock is used in the c

The internal clock is used in the clock circuit design. The internal oscillation circuit is used. The external timing element is connected to xtal1 and xtal2 pins of 51 single chip microcomputer. The internal oscillation circuit produces self oscillation. This design adopts the common internal clock mode, which is a parallel resonant circuit composed of external crystal and capacitor. A 20MHz oscillating crystal and 30pf capacitors are selected for the crystal. In order to improve the stability of capacitor model, NPO capacitor is selected.The reset circuit is designed to automatically reset by power on, because this reset method is relatively simple, and is realized by charging the capacitance of the external reset circuit. As long as the rising time of VCC does not exceed 1 millisecond, the power on reset can be realized. 20MHz for clock circuit, 10uF for reset circuit capacitance C and 4.7K for resistance