3.2.2晶振电路该晶振电路采用的是石英晶振，C3是石英晶振电容。晶振

3.2.2 Crystal oscillator circuit <br>The crystal oscillator circuit uses a quartz crystal oscillator, and C3 is a quartz crystal oscillator capacitor. The larger the crystal oscillator capacitance, the faster the microcontroller's response speed, so the crystal oscillator circuit is called the heart of the microcontroller. The anti-interference ability of the crystal oscillator circuit is strong when the response speed is slow, and the anti-interference ability is weak when the response speed is fast, so it is not that the faster the response speed, the better. The crystal oscillator circuit is a reliable, stable and high precision oscillator. The circuit can be connected to an external circuit to obtain high-precision sinusoidal alternating current, thus forming a sine wave oscillation. When the MCU works once, the MCU can execute multiple instructions. XTAL1 and XTAL2 are connected at both ends of the quartz capacitor. Capacitor C1 is connected to XTAL1 and capacitor C2 is connected to XTAL2. The two capacitors must be grounded. The sum of the two capacitors is equal to the load capacitance, as shown in the figure below. <br><br>Figure 3.2 Crystal oscillator circuit <br>3.2.3 Program download circuit <br>The first step of the microcontroller is to write the program, and the TTL level is used for the microcontroller. The TXD and RXD ports are TTL level, so the microcontroller converts the input TTL signal into RS232 signal for downloading or converts the output RS232 signal into TTL signal transmission. <br>It is closer to the factory use method, so the design is adopted. The first uses a serial interface to connect with the computer system, and the second uses MAX232 as a relay station to connect with the single-chip computer. MAX232 is a dual receiver and driver. The system that provides electrical signals is different from RS232 in that it converts signals through the MAX232 chip and transmits them to the single-chip microcomputer; it can also convert RS232 into electrical signals required by external systems. The program download circuit is shown in the figure.

3.2.2 Crystal Circuit<br>The crystal circuit uses quartz crystal, and C3 is a quartz crystal capacitor. The larger the crystal capacitor, the faster the reaction speed of its single-chip machine, so the crystal-vibration circuit is called the heart of the microcontroller. When the reaction speed of the crystal circuit is slow, its anti-jamming ability is strong, and its anti-jamming ability is weak when the reaction speed is fast, so the faster the reaction speed is better. The crystal circuit is a reliable, stable and high precision oscillator. The circuit can be externaled to obtain high-precision sine AC, thus forming sine wave oscillations. When a microcontroller works a single controller at a time, it can execute multiple instructions. XTAL1 and XTAL2 are connected to both ends of the quartz capacitor, the capacitor C1 connects xTAL1, the capacitor C2 connects XTAL2 and is grounded, the two capacitors add up to the load capacitor, as shown in the following figure.<br><br>Figure 3.2 Crystal circuit<br>3.2.3 Program Download Circuit<br>The first step of a microcontroller is to write to the program, and the TTL level is used for the microcontroller. The TXD and RXD ports are TTL levels, so the microcontroller converts the input TTL signal into rs232 signal for download or the output RS232 signal into TTL signal transmission.<br>Better proximity to the use of the factory, so the design is adopted. The first adopts a serial interface, connects with the computer system, and the second uses the MAX232 as a transit station function to connect with the microcontroller. The MAX232 is a two-set receiver and drive. Unlike the RS232, the system that provides the electrical signal is converted via the MAX232 chip and transmitted to a microcontroller, and the RS232 can also be converted into the electrical signal required by an external system. The program download circuit is shown in the figure.

3.2.2 crystal oscillator circuit<br>The crystal oscillator circuit adopts quartz crystal oscillator, and C3 is quartz crystal capacitor. The larger the crystal capacitor is, the faster the reaction speed of the single-chip microcomputer is, so the crystal oscillator circuit is called the heart of the single-chip microcomputer. When the reaction speed of crystal oscillator is slow, its anti-interference ability is strong, and when the reaction speed is fast, its anti-interference ability is weak, so it is not that the faster the reaction speed is, the better. Crystal oscillator circuit is a reliable, stable and high precision oscillator. The circuit can be connected to an external circuit to obtain a high-precision sinusoidal alternating current, thus forming a sinusoidal wave oscillation. When the single chip microcomputer works once, it can execute many instructions. Xtal1 and xtal2 are connected at both ends of the quartz capacitor. Capacitance C1 is connected to xtal1, and capacitance C2 is connected to xtal2 and to be grounded. The sum of the two capacitors is equal to the load capacitance, as shown in the figure below.<br>Figure 3.2 crystal oscillator circuit<br>3.2.3 program download circuit<br>The first step of MCU is to write program, and TTL level is used for MCU. The TXD and RXD ports are TTL level, so the single chip microcomputer converts the input TTL signal into RS232 signal for downloading or the output RS232 signal into TTL signal for transmission.<br>Better access to the way the factory is used, so the following design is adopted. The first uses serial interface to connect with computer system, and the second uses MAX232 as transfer station to connect with MCU. MAX232 is a dual receiver and driver. The system providing electrical signal is different from RS232 in that it converts the signal through MAX232 chip and transmits it to single chip microcomputer; it can also convert RS232 into electrical signal needed by external system. The program download circuit is shown in the figure.<br>