Spansion，M3，mb9bf218s USB0芯片功能实现主从切换功能（OTG），主机模式读取U盘的文件。从机模式虚拟串口。-Spansion, M3, MB9BF218S USB0 chip functions to achieve master-slave switching function (OTG), host interface U disk to read the file. Slave virtual serial port