对串行总线及其协议作了总结，然后在此基础上对USB协议进行了深

入的分析，并针对协议的要求，对字段、包、数据传输事务、数据切换同步以及错误

检测等的实现进行了详细设计

-On the serial bus and protocol are summarized, and then on the basis of the USB protocol conducted in-depth analysis, and the requirement for agreement on the field, including, data transmission services, data synchronization and error detection switch implementation designed in detail