USB uses a four-wire cable, two of which are serial channels for transmitting data, and two for powering downstream (Downstream) devices, for any connection that has been successfully connected. Mutually recognized peripherals will transmit data at the highest rate that both devices can support. The USB bus automatically switches from high speed to low speed in a compatible transmission mode depending on the peripheral conditions and the lock is locked at the appropriate rate. USB is a token-based bus. Similar to Token Ring networks or FDDI token-based buses. The USB host controller broadcasts a token, and the device on the bus detects whether the address in the token matches itself, and responds by receiving or transmitting data to the host. USB manages USB bus power by supporting suspend/resume operations. The USB system uses a cascading star topology consisting of three basic components: a host, a hub, and a functional device.
  The host, also known as the root, root or root hub, is installed on the motherboard or as an adapter card installed on the computer. The host contains the main controller and the root hub (Root Hub), which controls the data on the USB bus and To control the flow of information, each USB system can only have one root hub, which is connected to the main controller, and a computer may have multiple root hubs.
  A hub is a specific component of a USB structure that provides a point called a port to connect devices to the USB bus, detects devices connected to the bus, and provides power management for those devices, responsible for bus fault detection and recovery. . The line provides energy for the bus and provides energy for itself (from the outside).
  The functional device is connected to the bus via a port. USB can also be used as a Hub.