RS-232-C: Also known as standard serial port, it is the most commonly used serial communication interface at present. 1970, developed by American Electronics Industry Association (EIA) in conjunction with Bell system, modem manufacturer and computer terminal manufacturer, used for serial communication. 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 adopts the standard 25-core D plug and socket. Later, a simplified 9-core D socket was used on the PC. At present, 25-core plug sockets are rarely used in applications. Nowadays, computers generally have two serial ports: COM 1 and COM2. You can see the 9-pin D connector on the back of the computer. Nowadays, many mobile phone data lines or logistics receivers are connected to computers through COM ports.
RS-422: In order to improve the shortcomings of short communication distance and slow speed of RS-232, RS-422 defines a balanced communication interface, which increases the transmission speed to 10Mb/s, extends the transmission distance to 4,000 feet (when the speed is lower than 100kb/s), and allows the maximum connection of/kloc on the balanced bus. RS-422 is a one-way balanced transmission specification for single-machine transmission and multi-machine reception, and is named TIA/EIA-422-A standard.
RS-485: In order to expand the application scope, EIA formulated the RS-485 standard on the basis of RS-422 in 1983, which increased the multi-point bidirectional communication capability, that is, allowed multiple transmitters to connect to the same bus, increased the transmitter's driving capability and collision protection characteristics, and expanded the bus * * * mode range, and later named TIA/EIA-485.
Universal Serial Bus (USB for short) is a widely used interface specification on computers at present, and it is a new peripheral interface standard initiated by several major manufacturers such as Intel, Microsoft, Compaq, IBM, NEC and Northern Telcom. USB interface is a four-pin interface on the computer motherboard, with two pins in the middle transmitting data and two pins on both sides supplying power to peripherals. The USB interface is fast and easy to connect, and no external power supply is needed. The transmission speed is 12Mbps, and the latest USB2.0 can reach 480Mbps. The maximum length of the cable is 5 meters, and the USB cable has 4 wires, 2 signal wires and 2 power wires, which can provide 5 volt power supply. USB cables are also divided into shielded and unshielded types. The transmission speed of shielded cable can reach 12Mbps, which is more expensive, while the speed of unshielded cable is 1.5Mbps, but it is cheaper. USB can connect 127 devices in series at most; Support plug and play and hot plug.
RJ-45 interface is the most commonly used interface in Ethernet. RJ45 is a general name, which refers to a modular jack or plug with 8 positions (8 pins) standardized by IEC (60)603-7 and defined by the international connector standard.
The difference between serial port and parallel port;
The serial port is one channel, while the parallel port is eight channels, which can transmit eight bits (one byte) of data at the same time.
But the speed of parallel port is not fast, because 8-bit channels interfere with each other. Transmission is limited by speed. Moreover, when transmission errors occur, 8-bit data should be retransmitted at the same time. The serial port has no interference. Just resend one bit after transmission error. So it is faster than parallel port. This is the importance people attach to the serial hard disk.
Serial port of the switch:
The English for serial port of switch is trunk, which is used for next-hop routing conversion. VLAN can only be connected to external network after routing through trunk.
Pin description:
Pin name directory description
1 CD carrier detected
2 RXD receiving data
3 TXD transmission data
4 DTR data terminal is ready.
5 GND system grounding
6 DSR data set ready
7 send RTS request
8 CTS allows sending.
9 RI ring indicator