英语翻译USB data is transmitted by toggling the data lines betwe

英语翻译
USB data is transmitted by toggling the data lines between the J state and the opposite K state.USB encodes data using the NRZI convention; a 0 bit is transmitted by toggling the data lines from J to K or vice-versa,while a 1 bit is transmitted by leaving the data lines as-is.To ensure a minimum density of signal transitions,USB uses bit stuffing; an extra 0 bit is inserted into the data stream after any appearance of six consecutive 1 bits.Seven consecutive 1 bits is always an error.
A USB frame begins with an 8-bit synchronization sequence 00000001.That is,after the initial idle state J,the data lines toggle KJKJKJKK.The final 1 bit (repeated K state) marks the end of the sync pattern and the beginning of the USB frame.
A USB frame's end,called EOP (end-of-packet),is indicated by the transmitter driving 2 bit times of SE0 (D+ and D- both below max) and 1 bit time of J state.After this,the transmitter ceases to drive the D+/D− lines and the aforementioned resistors hold it in the J (idle) state.A receiver may take extra time to decode the SE0 state,and will see the first bit time as a repetition of the last data bit.Since USB frames are always a multiple of 8 bits long,this extra "dribble bit" can be detected and ignored.
A USB bus is reset using a prolonged (10 to 20 milliseconds) SE0 signal.
USB 2.0 devices use a special protocol during reset,called "chirping",to negotiate the High-Speed mode with the host/hub.A device that is HS capable first connects as an FS device (D+ pulled high),but upon receiving a USB RESET (both D+ and D- driven LOW by host for 10 to 20 mS) it pulls the D- line high.If the host/hub is also HS capable,it chirps (returns alternating J and K states on D- and D+ lines) letting the device know that the hub will operate at High Speed.
Clock tolerance is 480.00 Mbit/s ±500 ppm,12.000 Mbit/s ±2500 ppm,1.50 Mbit/s ±15000 ppm.
Though Hi-Speed devices are commonly referred to as "USB 2.0" and advertised as "up to 480 Mbit/s",not all USB 2.0 devices are Hi-Speed.The USB-IF certifies devices and provides licenses to use special marketing logos for either "Basic-Speed" (low and full) or Hi-Speed after passing a compliance test and paying a licensing fee.All devices are tested according to the latest spec,so recently-compliant Low-Speed devices are also 2.0 devices.
The actual throughput currently (2006) attained with real devices is about two thirds of the maximum theoretical bulk data transfer rate of 53.248 MB/s.Typical hi-speed USB devices operate at lower speeds,often about 3 MB/s overall,sometimes up to 10–20 MB/s.
USB defines class codes used to identify a device’s functionality and to load a device driver based on that functionality.This enables a device driver writer to support devices from different manufacturers that comply with a given class code.

USB数据传输的切换之间的数据线的J国和对面K状态.编码数据的USB接口使用NRZI公约; 1 0位是由切换的数据线从J至K或反之亦然,而1位是由离开数据线原样.为了确保最低密度的信号转换,USB接口使用比特填充;额外的0位是插入到数据流后,任何出现连续1位.连续7 1位始终是一个错误.
一个USB帧始于8位同步序列00000001 .这就是说,在最初的空闲状态J以来,数据线切换KJKJKJKK .最后1位（重复K国）标志着对同步模式,并开始的USB框架.
一个USB帧的目的,要求业（结束包） ,是所显示的发射机驾驶2位次SE0 （丁+和D -都低于最大值）和1位时间的J状态.在此之后,发射机停止硬盘的D + /名D -线和上述电阻举行它的J （空闲）状态.接收器可采取额外的时间来解码SE0状态,将看到的第一个位时间的重复过去的数据位.由于USB接口帧总是多的8位长,这个额外的“运球位”可以侦测和忽视.
一个USB总线重置利用长期（ 10至20毫秒） SE0信号.
USB 2.0设备使用特殊的协议重置期间,所谓的“唧唧” ,谈判高速模式与东道国/枢纽.有个装置,能够高速首次作为财政司司长连接设备（丁+退出高） ,但在接到一个USB复位（二者兼有d +和D -驱动低的东道国为10至20毫秒）它拉的D -线高.如果东道国/集线器也能高速,它啾（返回交替J和K国对D -和D +线）让设备知道该中心将在高速运行.
时钟宽容是四百八十零点零零兆位/秒± 500含量,12.000兆位/秒± 2500含量,1.50兆位/秒± 15000含量.
虽然高速设备通常被称为“的USB 2.0 ” ,并标榜“高达480兆位/秒的” ,并不是所有的USB 2.0设备的高速.USB - IF的认证装置,并提供授权使用特殊标志或者销售“基本法高速” （低速和全速）或高速后通过符合性测试,并支付许可费.所有的设备进行测试,根据最新的规格,所以最近兼容低速器件也是2.0设备.
目前的实际吞吐量（ 2006年）实现真正的设备是约三分之二的最大理论批量数据传输速率53.248手机/秒典型的高速USB的电子设备采用较低的速度,经常约3 MB / s的整体,有时多达10月20日手机/秒
USB接口定义类代码用于识别设备的功能,并加载设备驱动程序的基础上,功能.这使得设备驱动程序的作家,以支持不同厂商的设备符合某一类代码.