USART circuit design based on RS232 asynchronous serial communication

The AVR series of microcontrollers all have asynchronous serial interfaces, and the ATmega64 we are learning now has two serial ports. We know that the level of a microcontroller is generally TTL level, while the serial port of a computer is RS-232 level. These two levels cannot match each other, so if these two levels are interconnected, a level conversion circuit is needed. In this example, the commonly used MAX232 chip is used, which realizes the interchange of RS-232 levels and TTL levels. The AVR series of microcontrollers all have asynchronous serial interfaces, and the ATmega64 we are learning now has two serial ports. We know that the level of a microcontroller is generally TTL level (we will explain the difference between TTL level and other levels such as CMOS level in detail later), while the serial port of the computer is RS-232 level. These two levels cannot Match each other, so if these two levels are interconnected, a level conversion circuit is required. In this example, the commonly used MAX232 chip is used, which realizes the interchange of RS-232 levels and TTL levels. In the data sheet of MAX232, there is a typical connection circuit of this chip. We can just use this circuit directly. Regarding the connection circuit of MAX232, it is actually very simple. We only need to remember 4 capacitors (or 5 capacitors). The 4 capacitors here refer to the fact that only 4 capacitors need to be connected in the circuit; as for the 5 capacitors, the extra capacitor is the capacitor connected between VCC and GND. This capacitor does not need to be connected, but considering the stability of the power supply Speaking of which, I suggest you pick it up. As for the selection of capacitor size in the circuit, you can refer to the data sheet. It should be noted that non-polar capacitors are used here (no distinction between positive and negative poles). There are generally three choices for capacitance value: 0.1uF, 1uF, and 10uF. The size of the capacitance value will affect the driving ability of the port. Large capacitance means strong driving ability; small capacitance means weak driving ability. Usually a 1uF capacitor is enough. The RS-232 serial communication circuit diagram is as follows: