What is the rs232 serial port

The serial port is a very common device communication protocol on the computer. Electrical characteristics of the serial port: 1) RS-232 serial communication has a maximum distance of 50 feet; 2) RS232 can achieve two-way transmission, full-duplex communication, and the highest transmission rate is 20kbps. 3) The digital quantity transmitted on RS-232C adopts negative logic. , And symmetrical with ground, logic 1: -3 to -15V, logic 0: +3 to +15V. Let's learn more about the RS232 serial port information.

　　 The 9-pin interface behind the desktop computer is the com port (serial port), which is widely used in industrial control and data acquisition.

　　The rightmost is the serial port interface, collectively called RS232 interface　 ​​(package DB9)

　　Only two feet are involved in communication during communication

　　2 feet: computer input RXD

　　3 pin: the computer's output TXD can realize full-duplex (simultaneous sending and receiving) serial asynchronous communication through 2 and 3 pins

　　5 feet: ground

　　 RS232 pin circuit connection is completed (only three pins)

　　For MCU

　　 The P3 port of the single-chip microcomputer has two multiplexed interfaces, RXD and TXD. These are the transceiver ports for the serial communication of the single-chip microcomputer. The connection should be misaligned and correspond to the TDX RDX of the computer.

　　 Note: The level standards of single-chip microcomputer and rs232 are different (see another word for various level standards)

　　The level standard of the microcontroller TTL level: +5V means 1 0V means 0

　　 Rs232 level standard +15/+13 V means 1 -15/-13 means 0

　　 Therefore, the communication between the MCU and the computer serial port should follow the following connection methods:

　　The conversion between TTL level and RS232 level is realized through the level conversion circuit (Max232 chip in the top figure) between the MCU and the rs232 port given by the host computer

　　 PC serial port and MCU serial port connection diagram:

　　Pay attention to these two DB9s: DB91 is on the computer and DB92 is welded on the MCU experiment board

　　 The cross connection here means that the RXD of DB91 is connected to the TXD of DB92

　　 The RXD of DB92 is connected to TXD of DB91, cross-connected like this

　　If the computer does not have an rs232 port but only a USB port, you can use a serial port adapter cable to switch to a serial port 　 as shown in the figure:

　　 At this time, the driver needs to be installed on the upper computer of the computer

　　 Note that this driver drives the PL2303 chip (in the big head of the picture above) to convert RS232 information into usb information

　　 The following picture shows the internal structure of the above picture:

　　Using serial port communication is easier than USB because serial port communication has no protocol and it is easy to use

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