A typical USB connector application system consists of a USB host, a USB device and a USB cable. In the USB bus system, external devices are generally unified as USB devices, which mainly complete specific functions, such as commonly used U disk, mobile hard disk, mouse, keyboard, game controller, etc. The USB host is the master of the system and is responsible for the control and processing of data in the process of USB communication. During the transmission of the USB connector, the data transmission from the USB host to the USB device is called Down Stream communication, and the data transmission from the USB device to the USB host is called Up Stream communication.
Similar to the layered structure design of Ethernet, the bus system of USB connector also has a clear layered structure. That is, a complete USB application system can be divided into function layer, device layer and bus interface layer.
1. Function layer. The function layer is mainly responsible for the data transmission between the USB host and the device in the USB connector application system, which is composed of the function unit of the USB device and the corresponding USB host program. The functional layer provides four types of data transmission, including Control Transfer, Bulk Transfer, Interrupt Transfer and Isochronous Transfer.
2. Equipment layer. In the USB connector system, the device layer is responsible for managing the USB devices, assigning the addresses of the USB devices, and obtaining the device descriptors. The work of the device layer requires support for drivers, USB devices, and USB hosts. In the device layer, the USB driver can acquire the capabilities of the USB device.
3. Bus interface layer. The bus interface layer realizes the timing of USB data transmission in the USB connector system. USB bus data transmission uses NRZI coding, which is reverse non-return to zero coding. In the USB connector bus interface layer, the USB controller automatically carries out NRZI encoding or decoding to complete the data transmission process. The bus interface layer is usually completed automatically by the USB interface hardware.
Post time: May-31-2021