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Usb knowledge

                          Usb knowledge         

     USB, is the English Universal Serial Bus (Universal Serial Bus) abbreviation, is an external bus standard, used to regulate the computer and external devices connected and communication. Is applied in the PC field interface technology. The USB interface supports plug-and-play and hot-swapping of devices. USB at the end of 1994 by Intel, Compaq, IBM, Microsoft and other companies jointly proposed.

     The next generation USB interface will have the direction of change, the next generation of Type-C USB interface, can support both positive and negative plug, and the transmission of data signals, but the current (2014) manufacturers limited.

      As of December 26, 2015, many domestic manufacturers have been large-scale in their own production of mobile phone equipment manufacturers based on the use of the standard data lines.

     Since November 11, 1994 published USB V0.7 version, USB version has undergone many years of development, has developed into version 3.1, the twenty-first century computer standard expansion interface. The current (2016) motherboard is mainly used USB2.0 and USB3.0 interface, the USB version can be a very good compatibility. USB with a 4-pin (USB3.0 standard for the 9-pin) plug as a standard plug, daisy chain can be used to connect all the peripherals, up to 127 external devices can be connected, and will not lose bandwidth. USB requires host hardware, operating system and peripherals in three areas to support work. Twenty-first century motherboards are generally used to support the USB function of the control chipset, the motherboard is also equipped with a USB interface socket, and in addition to the backplane socket, the motherboard also reserved USB pin, you can connect through the connection To the front of the chassis as a front USB interface to facilitate the use of (Note, in the wiring to carefully read the motherboard manual and according to map connection, do not connect the wrong equipment damage). And the USB interface can also be through a dedicated USB cable to achieve dual-machine interconnection, and can be extended through the Hub more interfaces. USB has the advantages of fast transmission speed, easy to use, hot plug, flexible connection, independent power supply, etc., can connect mouse, keyboard, printer, scanner, camera, charger, flash drive, MP3 player, mobile phone, digital camera, mobile Hard drive, external drive / floppy drive, USB card, ADSL Modem, Cable Modem, etc., almost all of the external equipment.

      Theoretically the USB interface can be used to connect up to 127 peripherals such as mice, modems and keyboards. Since its launch in 1996, USB has been successful in replacing serial and parallel ports and has become one of the necessary interfaces for personal computers and large numbers of smart devices in the 21st century.

      The main controller is responsible for the transmission of data streams between the host and the USB device. These transmission data are treated as consecutive bit streams. Each device provides one or more interfaces that can communicate with the client program, each consisting of 0 or more pipes that independently transmit data between the client program and the specific terminal of the device. USBD establishes the interface and the pipeline for the actual needs of the host software. When the configuration request is made, the main controller provides the service according to the parameters provided by the host software.

      USB supports four basic data transfer modes: control transmission, isochronous transmission, interrupt transmission and data block transfer. Each transmission mode is applied to a terminal with the same name, and has different properties.

     Control the transmission type

     Support between the peripherals and the host control, status, configuration and other information transmission, between the peripherals and the host to provide a control channel. Each peripheral supports control of the transmission type, so that between the host and the peripherals can send configuration and command / status information.

     Isochronous (lsochronous) transmission type (or synchronous transmission)

     Supports data transfer between peripherals and hosts with periodic, limited latency and bandwidth and constant data transfer rates. This type of error-free verification, it can not guarantee the correct data transmission, support like computer - telephone integrated system (CTI) and audio system and host data transmission.

     Interrupt the transmission type

     Supports input devices such as game handles, mice and keyboards, which are small in size and non-cyclical, but are responsive to response time and require immediate response.

     Data block (Bulk) transmission type

     Support for printers, scanners, digital cameras and other peripherals, these peripherals and the amount of data transmitted between the host, USB bandwidth to meet the case of the type of data transmission.

     USB uses a split bandwidth allocation scheme that can not enter the device if the peripherals exceed the current bandwidth allocation or potential requirements. Synchronize and interrupt the transmission type of the terminal to retain the bandwidth and ensure that the data is transmitted at a certain rate. The centralized and control terminals transmit the transmission data according to the best available bandwidth.

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