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The hardware structure of USB
TIME:2016-09-17 09:12
USB uses four cables, which is used to two serial channel to transmit data, the other two downstream (Downstream) equipment to provide power for high speed and high bandwidth peripherals, USB to transmit data at full speed 12Mbps; for low-speed peripherals, USB with 1.5Mbps transmission rate of data transmission.

The USB bus can be automatically converted automatically according to the condition of the peripheral equipment in the two transmission modes. USB is based on token bus. Token ring network or FDDI token based bus. USB host controller broadcast token, the device on the bus to detect the address of the token is consistent with their own, by receiving or sending data to the host to respond. USB manages the USB bus power supply by supporting the suspension / resume operation. The USB system uses level Lianxing topology, the topology consists of three basic components: the host (Host), the hub (Hub) and functional device.

The host, also known as the root, root node or root Hub, do it on the motherboard or as an adapter is installed on the computer, the mainframe comprises a main controller and a root hub (RootHub), control data and control information on the USB bus flow, each USB system can only have a root set line. It is connected with the main controller.

The hub is a specific component in the USB structure, it is called port (Port) of the equipment will be connected to a USB bus, and detection devices on the bus, and these devices provide power management, fault detection and recovery for the bus. Hub can provide energy for the bus, can also provide energy for their own (obtained from the external power supply), its energy equipment can be inserted into the bus hub to provide energy, but the downstream port bus provides energy equipment can't insert itself hub or support energy of more than four, such as the need to provide energy equipment over the bus 100mA power, not the same bus power supply hub connection.

Functional device is connected to the bus through the port. USB also can do Hub use.
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