COM port is a serial communication port. The com port on a microcomputer is generally 9 pins and 25 pins, and the maximum speed is 1 15200bps. Usually used to connect a mouse (serial port) and communication equipment (such as connecting an external modem for data communication or CNC interface of some factories). Generally, there is only one COM port outside the motherboard. The nine-hole output (trapezoid) at the back of the chassis and the parallel port is COM 1 port, and the COM2 port is generally led out from the motherboard. Parallel port is the longest trapezoidal port.

But at present, mainstream motherboards generally only have 1 serial port, or even no serial port, which will gradually be replaced by USB.

The interface standard specification and bus standard specification of COM port are RS-232, sometimes called RS-232 port.

Pin diagram of 9-pin serial port

Pin function of 9-pin serial port:

Pin function

1 carrier detection (CD)

2 received data (RXD)

3 send data (TXD)

4 Data Terminal Ready (DTR)

5 Signal ground wire (SG)

6 data ready (DSR)

7 request to send (RTS)

8 Clear Send (CTS)

9 Ringing indication (RI)

25-pin interface definition:

Pin 1 protective ground

Pin 2 transmits data.

Pin 3 receives data.

Pin 4 request to send

Pin 5 allows transmission.

Pin 6 data set ready

Pin 7 signal ground

Pin 8 receives the line signal detector

(Data Carrier Detection)

Pin 20 data terminal ready

22-pin ring indicator

RS-232(ANSI/EIA-232 standard) is a serial connection standard on IBM-PC and its compatible computers. It can be used for many purposes, such as connecting a mouse, printer or modem, and it can also be connected to industrial instruments. In order to improve the driving and wiring, the transmission length or speed of RS-232 often exceeds the standard value in practical application. RS-232 is limited to point-to-point communication between PC serial port and equipment. The longest distance of RS- 232 serial communication is 50 feet.

-DB-9 pin connector

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\ 1 2 3 4 5 /

\ 6 7 8 9 /

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Cross section of the line connected from the computer. Function of RS-232 pin: data: TXD (pin 3): serial data output RXD (pin 2): serial data input handshake: RTS (pin 7): data transmission request CTS (pin 8): clear transmission DSR (pin 6): data transmission ready DCD (pin 1): data carrier detection DTR (pin 4 Data Terminal Ready Ground Wire: GND(pin 5): Ground Wire Other RI(pin 9): Ringtone Indication Note: COM interface is a physical port following RS232 standard. COM port refers to the physical realization of serial port, and RS232 is a serial port interface standard.