serial port
Serial port (Serial port), also known as serial interface or serial port, serial communication interface, COM interface, referred to as. It is mainly used for serial bit-by- bit data transmission. The common ones are RS-232 for general computer applications (using 25-pin or 9-pin connectors) and half-duplex RS-485 and full -duplex RS-422 for industrial computer applications .
Male DE-9 connector
Specification
Serial interfaces are classified according to electrical standards and protocols, including RS-232-C, RS-422, RS485, USB , etc. The RS-232-C, RS-422 and RS-485 standards only stipulate the electrical characteristics of the interface, and do not involve connectors, cables or protocols. USB is a new interface standard developed in recent years, mainly used in the field of high-speed data transmission.
- RS-232-C
Also known as standard serial port, it is the most commonly used serial communication interface at present. It is a standard for serial communication formulated by the American Electronics Industries Association (EIA) in conjunction with Bell System , modem manufacturers and computer terminal manufacturers in 1970 . Its full name is "Technical Standard for Serial Binary Data Exchange Interface between Data Terminal Equipment (DTE) and Data Communication Equipment (DCE)". The traditional RS-232-C interface standard has 22 wires and uses a standard 25-core D-type plug socket. The simplified 9-core D-type socket has been used since IBM PC/AT. So far, the 25-pin socket has been rarely used in modern applications. Computers generally have two serial ports: COM1 and COM2, and the 9-pin D-shaped interface is usually seen on the back of the computer. Now there are many mobile phone data lines or logistics receivers that use COM ports to connect to computers.
- RS-422
In order to improve the shortcomings of short communication distance and low rate of RS-232, RS-422 defines a balanced communication interface, which increases the transmission rate to 10Mb/s and extends the transmission distance to 4000 feet (when the rate is lower than 100kb/s), And allows up to 10 receivers to be connected on a balanced bus. RS-422 is a one-way, balanced transmission specification for single-machine transmission and multi-machine reception, named TIA/EIA-422-A standard.
- RS-485
In order to expand the scope of application, EIA formulated the RS-485 standard on the basis of RS-422 in 1983, adding multi-point and two-way communication capabilities, that is, allowing multiple transmitters to be connected to the same bus, while increasing the transmitter The driving ability and conflict protection characteristics of the bus extend the common mode range of the bus, and it is named after the TIA/EIA-485-A standard.
- Universal Serial Bus
Abbreviated as USB , it is an interface specification widely used on computers at present. It is a new peripheral interface standard initiated by several major manufacturers such as Intel, Microsoft, Compaq, IBM, NEC, and Northern Telcom. The USB interface is a four-pin interface on the computer motherboard, in which the two pins in the middle transmit data, and the two pins on both sides supply power to peripherals. The USB interface is fast, easy to connect, does not require an external power supply, the transmission speed is 12Mbps, and the new USB 2.0 can reach 480Mbps; the maximum length of the cable is 5 meters, and the USB cable has 4 lines: 2 signal lines, 2 power lines, which can be provided 5 volt power supply, USB cables are divided into two types: shielded and unshielded, the transmission speed of shielded cables can reach 12Mbps, the price is more expensive, the speed of unshielded cables is 1.5Mbps, but the price is cheap; USB can connect up to 127 devices in series ; Support hot swap. The latest specification is USB 4.0 with a maximum transfer speed of 40 Gbps.
- RJ-45 interface
It is the most commonly used interface for Ethernet. RJ45 is a commonly used name, which refers to a modular jack that is standardized by IEC (60) 603-7 and uses 8 positions (8 pins) defined by international connector standards or plug.
Difference from parallel port
Similar to a lane, a parallel port means that there are 8 lanes that can transmit 8 bits (one byte) of data at the same time. But it is not parallel port fast, due to mutual interference between 8-bit channels. The speed of transmission is limited. Moreover, when a transmission error occurs, 8 bits of data must be retransmitted at the same time. The serial port has no interference, and it is enough to resend one bit after a transmission error, so it is faster than the parallel port.
switch
The English name of the switch is trunk; it is used for next-hop routing conversion. Each VLAN can access the external network only after it is pointed to by the route with TRUNK
Actual usage instructions
Pin Name Dir Description 2 TXD OutPut Transmit Data 3 RXD InPut Receive Data 5 GND System Ground 7 CTS InPut Clear to Send 8 RTS OutPut Request to Send 9 Vcc InPut Power Supply(+5V)
use
On the computer motherboard: the interface for serial transmission, which can only transmit 1Bit at a time. The serial port can be used to connect an external modem, plotter, or serial printer. It can also connect to network devices, such as routers and switches, as a console connection, mainly to configure them. Consumer electronics have replaced serial ports by USB ; but in non-consumer applications, such as network equipment, serial ports are still the main transmission control method.
- Terminal (Computer terminal).
- Modems (Dial-up modems).
- Printers .
- Network equipment ( routers , switches, etc.).
- Old style serial port mouse .
- Old rocker .
- GPS receiver (4800 bit/s for NMEA 0183 standard).
- An old GSM mobile phone .
- Satellite phones , low-speed satellite data machines and other satellite transmission equipment, etc.
- Programmable writers such as microcontrollers and EPROMs.
- Barcode scanners or other point-of-sale intelligence (POS) devices.
- LED or LCD text display.
- Self-made electrical equipment, industrial electrical equipment.
- Old style digital camera .
- Measuring instruments, such as digital multi-function meters, oscilloscopes , etc.
- Used by consumer electronics products to update firmware .
Communication methods include synchronous communication and asynchronous communication.
- Synchronous communication: Under the agreed communication rate, the clock signal frequency and phase of the sending end and the receiving end are always synchronized to ensure that the two parties in communication have exactly the same timing relationship when sending and receiving data.
- Asynchronous communication: also known as start-stop asynchronous communication, which is transmitted in units of characters. There is no fixed time interval requirement between characters, and each bit in each character is transmitted at a fixed time.
see