How does a microcontroller communicate with a computer? Electronic engineers must know

The serial port of the microcontroller is TTL level and cannot communicate directly with the computer. Level conversion is required. There are many types of level conversion chips on the market. Today I recommend three types to you, namely MAX232, CH340G, and CH340C. The following are introduced respectively.

1. MAX232 chip

This chip is a chip that appears frequently. Whether it is in university textbooks or on MCU development boards, as long as it involves USB/serial ports, this chip will definitely be mentioned. This chip has a dual-channel conversion interface, and the circuit design is not complicated. The following figure is a typical design schematic:

Typical schematic diagram of MAX232 chip

This chip requires four capacitors to build peripheral circuits. The manual recommends using 1uF polarized capacitors, but it has been verified that 0.1uF capacitors can also be used, which greatly reduces the size of the board.

2. CH340G chip

CH340G is produced by Nanjing Qinheng. It can be said that the level conversion chips and gateway chips produced by this company are all magical tools, with simple peripheral circuits and powerful functions. CH340G chip is currently selling well due to its simple peripheral circuits and is often out of stock. Its typical schematic diagram is shown below:

CH340G typical schematic diagram

This chip needs an external 12M crystal oscillator, and when designing, please note that the processing method of the 4th pin V3 is different when the external power supply is 5V and 3.3V. In the above figure, when the external power supply is 5V, V3 needs to pass through a 0.1uF capacitor to GND; when the external power supply is 3.3V, V3 needs to be connected to the power supply. At present, many USB to serial port modules are designed using this chip.

USB/TTL Module

The currently popular ISP automatic download circuit uses this chip.

3.CH340C chip

CH340C and CH340G are in the same series, but CH340C can save the external 12M crystal oscillator and oscillator capacitor when used, saving PCB space and cost, and is relatively more convenient to design. The typical circuit schematic of CH340C is shown below:

CH340C typical schematic diagram

The prices of these chips are not very high, CH340G is about 1.8 yuan, CH340C is about 1.94 yuan, and MAX232 is about 3 yuan. Of course, there are many other chips such as PL2303, which are not recommended here.