"Interface" "USB" 1. Study notes

1, The advantages of USB:	The can be hot-swappable, which can be automatically recognized when plugged in,              System bus powered, usb d+ line, a d- line, d+ and d- line is a differential input line; The can support multiple devices, and it is easy to extend through hub You can connect more than one device to another host Transmits data fast, up to 480mbit/s Convenient device interconnection: In the absence of a host, to achieve point-to-point communication (also can achieve master-slave interchange) (USB OTG )
2 usb Basic specification:	Usb1.0/1.1       low-speed keyboard, mouse, etc.                   Full Speed situation 12mbit/s : u disk, cd-rom Usb2.0           High speed reach 480mbit/s : Audio devices, displays, etc. Usb otg         Device-to-device transport
3,USB device class specification:	Mass Storage Equipment Class (Mass Storagedevice)U - disk,CD-ROM , etc. Human-Computer Interaction equipment (Human Interfacedevice) keyboard, mouse, gamepad Voice Devices (audiodevice) microphones, stereos, etc. Communication Device Class (communicationdevice) telephone, modem, etc. Printer Equipment Class (Printerdevice) printer Monitor device classes (Monitor devices) monitors, cameras, etc.
4,theUSB logic is divided into : Signal layer, protocol layer, data transfer layer	Protocol layer: A packet is the basic unit of information transmission in a USB system, and all data is packaged and transmitted over the bus. Package by 6 part: Synchronization field ( Span style= "font-family: ' Times New Roman ';" >sync pid addr Span style= "font-family: the song Body;" ); Data fields ( data ); Inspection fields ( CRC ); Package End ( Span style= "font-family: ' Times New Roman ';" >eop Package identifier (PID): Token pack(token) (output, input, frame start, build), data packet(data) , data 1 ), handshake Pack (handsnake) (confirm, not confirm, stop), special package ( Special ) (pre-sync)
5, usb " Span style= "font-family: the song Body;" The agreement provides 4 data transfer mode:	Control Transport: burst, non-cyclical, host initiated, Transport for command and status Synchronous transmission: Periodic, continuous transmission for transmission of aging-related information, and information on storing timestamps in data Interrupt Transmission: Periodic, low frequency, allow limited latency communication Large-capacity data transfer: Non-cyclical, high-volume burst traffic
6.USB Descriptor:	1) Device Descriptor: Describes the type of device, vendor information,the type ofUSB Protocol, the maximum length of the report data for the endpoint, and so on, each USB device has only one device Descriptor 2) Configuration descriptor: Each configuration descriptor provides a device-specific configuration that describes the nature of the interface and endpoint of the device, the power supply mode, and the consumption of the device 3) Interface Descriptor: Describes the characteristics of different interfaces of the device, for example, the function of a device U -disk, and the function of the keyboard, with two interface descriptors to describe two functions respectively 4) String Descriptor: Describes the device manufacturer, device name, what serial number and other information

"Interface" "USB" 1. Study notes