RS-232 interface is also called RS-232 port, serial port, asynchronous port or COM (communication) port. "RS-232" is its clearest name. In the computer world, a large number of interfaces use serial ports for data connection, and the connected hardware is an RS-232 nine-core cable. To make an RS-232 serial port cable, you must first understand the pin description of the RS-232 serial port. RS-232 serial ports are divided into 9-pin serial ports (commonly known as male) and 9-hole serial ports (commonly known as female).
The respective pin descriptions are as follows:
1. RS-232 port (DB9 male/pin type) pin definition:
Pin number: 2 3 5
Signal definition: RXD TXD ground
2. RS-232 port (DB9 female/hole type) pin definition: (Because the serial port on the back of the computer is mostly male, this female can be directly inserted into the computer’s COM port for connection)
Pin number: 2 3 5
Signal definition: TXD RXD ground
Knowing the pin standards of the male and female RS-232 ports, making the data line becomes quite simple. From the figure, you can notice that the pin definition sequence of the male and female pins is just the opposite. After paying attention to this point, the serial port data line is made as follows:
1: Connection method of male and male connector: (COM ports between different computers are connected in this way, at this time, both ends of the serial cable use female connectors)
COM1 male 2——Data line female 2—(data line) —Data line female 3 —COM2 male 3
COM1 male header 3-data line female header 3-(data line)-data line female header 2-COM2 male header 2
COM1 male header 5-data line female header 5-(data line)-data line female header 5-COM2 male header 5
It can be seen from the above data flow that the data lines connecting the COM ports of the two computers are female at both ends, and the internal pins are crossed. As a result of the data line connection, the data pins of the two external computer COM ports are also crossed: that is, two or three crosses, and five to five connections. In this way, the asynchronous full-duplex serial communication mode of the COM port between the two computers is realized.
2: Connection method of male and female connectors: (Some experimental development boards use female connectors for the serial port. This connection method is generally used to connect the COM port of a computer to other external devices.)
Computer COM1 male connector 2-data cable female connector 2-(data cable)-data cable male connector 2-development board COM2 male connector 2
Computer COM1 male connector 3-data line female connector 3-(data cable)-data line male connector 3-development board COM2 male connector 3
Computer COM1 male connector 5—Data cable female connector 5—(Data cable)—Data cable male connector 5—Development board COM2 male connector 5
It can be seen from the data line connection that the internal pins of the data line are not crossed. This is because the pin functions of the female and male headers are relative, so there is no need to cross. This kind of connection shows externally that the data pins of the computer COM1 male connector are connected to the COM2 female connector of the development board without cross.
In short: the connection method of the data cable only needs to remember one point: the same head should be crossed, and different heads should not be crossed. This is determined by the pin descriptions of the male and female headers.
