One. USB basic knowledge
USB is the abbreviation of English Universal Serial Bus, and the meaning of Chinese is a "universal serial bus". In 1994, in 1994, seven world-renowned computer and communication companies such as Intel, Compaq, NEC, Northern Telecom have set up a USB Forum, spent nearly two years, has formed a unified comment, November 1995 The USB0.9 Universal Serial Bus specification was formally established. In 1997, there was a periphement that truly met USB technical standards. USB1.1 is currently launched in a standard in supporting USB computers and peripherals. At the beginning of the INTEL's Development Forum in 1999, participants introduced USB2.0 norms. In addition to the original Compaq, Intel, Microsoft and NEC, there are HP, Lucent and Philips in addition to the original Compaq, Intel, Microsoft and NEC. new member. USB2.0 is compatible downwardly USB1.1, the transfer rate of data will reach 120Mbps ~ 240Mbps, and also supports wideband wide digital camera and next-generation scanners, printers, and storage devices.
The currently used USB1.1 is mainly applied to the medium and low speed external equipment, which provides the transmission speed of 1 .5Mbps and full speed 12Mbps, low speed USB bandwidth (1.5Mbps) supports low speed devices, such as displays, modems, Keyboard, mouse, scanner, printer, optical drive, tape drive, floppy drive, etc. Full speed USB bandwidth (12Mbps) will support a wide range of multimedia devices.
USB can be widely supported and rapidly popular, because it has many of the features:
1. Ease of use of end users
● Provide a single model for the cable and connecting head
● Electrical characteristics are not related to users
● Self-test, automatic device driver and setting
● Peripherals can be dynamically connected, dynamically reset
2. Widely applicability
● Adapt to different equipment, transmission rate from several Kb / s to more than ten MB / S
● Support synchronization, two transmission modes on the same line
● Support for multiple devices
● 127 physical devices can be operated simultaneously
● Multiple data and information flow can be transmitted between host and devices
● Support multifunctional devices
● Use the underlying protocol to improve bus utilization
3. Synchronous transmission bandwidth
● Determined bandwidth and low delay suitable for telephone systems and audio applications
● Synchronous work can be used to use the entire bus
4. Flexibility
● Send a series of specified sizes directly, allowing selection of device buffer sizes
● Supports various data transfer rates by specifying the size and execution time of the data buffer
● Buffering the data stream through the protocol
5. Rapidity
● Use an error handling / error recovery mechanism in the protocol
● Completely swappable in real time
● Can identify defective equipment
6. Consistency with the PC industry
● Easy and integrity of protocol
● Consistent with the Plug and Play architecture of the PC
● There is a good connection with the existing operating system.
7. Value
● Provide subchannels with a transmission rate of 1.5Mb / s at a low price
● Optimized integration of peripherals and host hardware
● Promote the development of low-cost specialization
● Cheap cable and connecting head
● Use commercial technology to reduce costs
8. Upgradeability
● Upgradeability of architecture supports multiple USB host controllers in one system
