USB Bus Structure

A usb system consists of three parts: USB host, USB device, and USB interconnect. USB interconnection refers to the connection and communication between the USB device and the host. It includes the bus topology, tasks and relations at each layer of communication, and data stream models, and bandwidth allocation when the host communicates with multiple USB devices.

USB is a Master/Slave Device. Data exchange can only happen between the host and the device. Only one host is allowed. Usb otg this USB extension specification allows a port to be used either as a host or as a device, and determines whether the host or device depends on which end of the USB cable is inserted into the device.

The physical connection of USB is a layered star topology with the hub in the center of each star. Each line is a point-to-point connection between a host and a hub or feature device, or between a hub and another hub or feature device ., The topology of the USB Bus is described. Due to the timing limitations of signal transmission in the hub and cable, the maximum number of layers of the star topology is 7 (including the root layer ). In this layer-7 structure, the communication path between the host and any device can support up to five non-root hubs. A compound device (as shown in 1) occupies two layers. Therefore, if it is connected to layer 7th, it cannot run. layer 7th can only connect to functional devices. A usb master controls that can connect up to 127 peripherals (including the root hub ).

USB topology