The STC89C52 has a high gain invert

The STC89C52 has a high gain inverter amplifier to train the oscillator. The RXD and TXD pins are the input and output of the amplifier. Watches can be created inside or out. The internal clock circuit is shown in figure 2.3 (a). When the external synchronization components are connected to the RXD and TXD pins, the internal oscillator will vibrate automatically. The time element typically uses a parallel resonant circuit consisting of a crystal and a capacitor. The crystal oscillation frequency can be selected in the range of 1.2 ～ 12mhz and the power value can be selected in the range 5 30pf. Frequency can be adjusted according to size of power value. The external clock circuit is shown in figure 2.3 (b). RXD is connected by quality and TXD is connected to an external oscillator. There are no special requirements for external oscillating signals, only pulse amplitudes are required. Typically, a square wave with a frequency lower than 12 MHz is used. The on-chip clock generator divides the oscillation frequency by 2 to produce a two-phase clock P1 and P2 that will be used in the microcontroller.As shown in the picture, the RXD is connected to the quality and the TXD is connected to the external oscillator. There are no special requirements for external oscillating signals, only pulse amplitudes are required. Typically, a square wave with a frequency lower than 12 MHz is used. The on-chip clock generator divides the oscillation frequency by 2 to produce a two-phase clock P1 and P2 that will be used in the microcontroller. RXD is connected by quality and TXD is connected to an external oscillator. There are no special requirements for external oscillating signals, only pulse amplitudes are required. Typically, square wave signals less than 12 MHz are used. The on-chip clock generator divides the oscillation frequency by two to create a two-phase clock P1 and P2 for use by the microcontroller.