浏览次数：2217次 发布日期：2021-12-09

 1. USB is a universal serial bus, which is a new serial interface supporting plug and play. It is also called "daisy chaining" because it has the ability to link 127 devices on a "cable". USB is much faster than the standard serial port, and its data transmission rate can reach 480MB per second (compared with 115kb per second for the old serial port).  
 
2. It should be noted that this is not a new bus standard, but an input / output interface standard for the computer system to connect peripheral devices (such as keyboard, mouse, printer, etc.). Up to now, there is no unified standard for the interface between the computer system and peripheral devices. For example, the socket of the keyboard is round, the 9-pin or 25-pin parallel interface is used to connect the printer, and the 9-pin or 25-pin serial interface is used for the mouse. USB can unify these different interfaces, using only a 4-pin plug as the standard plug. Through this standard plug, all peripherals can be connected in the form of daisy chain without losing bandwidth. USB is replacing the serial port and parallel port on the current PC.  
 
3. USB specification divides USB into five parts: controller, controller driver, USB chip driver, USB device and driver for different USB devices.  
(1) Controller. It is mainly responsible for executing the commands issued by the controller driver.  
(2) Controller driver. Establish a communication channel between the controller and the USB device.  
(3) USB chip driver. Provides support for USB.  
(4) USB device. Includes USB peripherals connected to the PC.  
 
4. At present, there are two other I / O port standards, one is IEEE1394 (also known as "FireWire" --- FireWire), and the other is devicebay. They are all "direct opponents" of USB.  
 
5. The disadvantage of USB is that it must be connected with PC and can not work independently without PC, and the transmission speed of version 2.0 is 480MB, which has reached the limit His opponent IEEE1394 can do it, and the speed can reach more than 1G.