实用USB术语详解。USB是一种“主-从”式总线，包括一个主机和多个从机。从机称作外设，在USB术语中也称作功能部件。主机称作主设备。所有USB传输都由主机启动；外设总是响应传输，不会启动传输。最常用的主机是PC机，主机通过USB-A连接器连接到下行设备。嵌入式主机不包括PC机，而是用一个微控制器作为专用主机，或许只能与一类USB设备通信。-Detailed practical USB terminology. USB is a " main- from the"　bus-style, including a host and a number from the machine. Peripherals from the machine called in the jargon, also known as USB features. Host called the main equipment. All USB transfer by the host to start　peripherals is always in response to transmission, will not start the transmission. The most commonly used are the host PC, the host through the USB-A connector to connect to the downstream equipment. Does not include embedded host PC, but with a dedicated microcontroller as the host, perhaps only with one type of USB device communication.