The internal clock circuit is the e

The internal clock circuit is the external timing element on the RXD and TXD pins, and the internal oscillator will produce self excitation oscillation. The parallel resonant circuit composed of quartz crystal and capacitor is usually used as timing element. The frequency of crystal oscillation can be selected between 1.2 and ± 12Mhz, and the capacitance value can be between 5 ~ 30pf. The size of capacitance value plays a certain role in the fine-tuning of frequency.