The communication interface on the PC has a USB interface, and the corresponding level logic conforms to the USB principle; there is also a DB9 interface (nine-pin port), and the corresponding level logic conforms to the RS-232 principle.
The serial communication on our MCU passes through the four pins of RXD, TXD, VCC and GND of the MCU, and the corresponding level logic complies with the TTL principle.
Of course, the learning board on the novice Xiaobai must have integrated USB to TTL chips like PL2303 and CP2102, and the corresponding interface has also become a USB interface; some learning boards integrate TTL to RS such as MAX232. -232 chip, the corresponding interface has also become a DB9 interface.
The purpose of the conversion is to convert the level to both sides. The following classification example:
Case 1: PC USB port communicates with MCU without level shifting chipMethod: Take out the USB to TTL module, as shown below. One end of the module is connected to the USB interface of the PC, and the other end has five pins of TXD, RXD, GND, 5V, and 3.3V, which are respectively connected to the RXD, TXD, GND, and 5V pins of the single chip microcomputer, and are powered by 3.3V. The one-chip computer can change 5V to 3.3V. The core of the module is a PL2303, CP2102 chip for USB and TTL level conversion.
Method : Connect directly with USB cable, but the USB interface form on the MCU sometimes differs. Select the appropriate wiring according to A-USB, B-USB, micro-USB, mini-USB respectively.
Case 3: PC USB port communicates with MCU integrated with TTL to RS-232 chipMethod : Purchase USB to RS-232 module, as shown below. The core of the module is a CH340 or CH341 level-shifting chip at the end of DB9 that converts RS-232 levels to USB levels.
Method: Outsourcing RS232 to TTL module, as shown below. One end of the module is DB9 connected to PC DB9, and one end is RXD, TXD, VCC, GND and the corresponding pin connection of the MCU. At its core is a max232 level conversion chip.
Method : Generally, the communication will not be done on the PC. The DB9 interface has a USB interface. If you have to do it, buy the RS-232 to USB module, as mentioned above.
Case 6: PC DB9 interface communicates with a microcontroller that becomes an RS-232 to TTL chipMethod : Connect directly with DB9 (serial cable)!
Use a picture to summarize a few things:
Finally, don't forget to install the appropriate driver on the PC side!
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