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请问如何识别high speed的USB设备 |
| 作者：debugme 栏目：嵌入式系统 |
请问如何识别high speed的USB设备 full speed 与low speed的usb 的识别分别在D＋、D－上上拉1.5K的电阻，使得信号由低变高识别，那high speed 的usb设备是怎么识别的呢？？？难道是在D＋上下拉1.5K，但是这样，信号线的电平没有任何变化，那么怎么识别呢？？？请高手指点 |
| 2楼： | >>参与讨论 |
| 作者： debugme 于 2007/1/17 9:43:00 发布：
请问二楼怎么通过线性调频脉冲来识别的，能详一下吗，谢谢 |
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| 3楼： | >>参与讨论 |
| 作者： computer00 于 2007/1/17 13:53:00 发布：
HUB首先发送一个JK序列，并切换到高速模式,设备收到后，也切换 到高速模式.如果没有，则保持在全速模式. 自己找USB2.0协议看看吧. High-speed Detection Handshake (not performed if low-speed DEVICE detected by hub): Note: In the following handshake, both the hub and DEVICE are required to detect Chirp J’s and K’s of specified MINIMUM durations. It is strongly recommended that “gaps” in these Chirp signals as SHORT as 16 high-speed bit times should restart the duration timers. 4. The high-speed DEVICE leaves the D+ pull-up RESISTOR connected, leaves the high-speed terminations disabled, and drives the high-speed signaling current into the D- LINE. This creates a Chirp K on the bus. The DEVICE chirp must last no less than 1.0 ms (TUCH) and must end no more than 7.0 ms (TUCHEND) after high-speed Reset time T0. 5. The hub must detect the DEVICE chirp after it has seen assertion of the Chirp K for no less than 2.5 Μs (TFILT). If the hub does not detect a DEVICE chirp, it must continue the assertion of SE0 until the end of reset. 6. No more than 100 Μs (TWTDCH) after the bus leaves the Chirp K state, the hub must begin to send an alternating sequence of Chirp K’s and Chirp J’s. There must be no Idle states on the bus between the J’s and K’s. This sequence must continue until a time (TDCHSE0) no more than 500 Μs before and no less than 100 Μs before the end of Reset. (This will guarantee that the bus remains active, preventing the DEVICE from entering the high-speed Suspend state.) Each individual Chirp K and Chirp J must last no less than 40 Μs and no more than 60 Μs (TDCHBIT). 7. After completing the hub chirp sequence, the hub asserts SE0 until end of Reset. At the end of reset, the hub must transition to the high-speed Enabled state without causing any transitions on the data LINEs. 8. After the DEVICE completes its chirp, it looks for the high-speed hub chirp. At a MINIMUM, the DEVICE is required to see the sequence Chirp K-J-K-J-K-J in order to detect a valid hub chirp. Each individual Chirp K and Chirp J must be detected for no less than 2.5 Μs (TFILT). a) If the DEVICE detects the sequence Chirp K-J-K-J-K-J, then no more than 500 Μs (TWTHS) after detection, the DEVICE is required to disconnect the D+ pull-up RESISTOR, enable the high-speed terminations, and enter the high-speed Default state. b) If the DEVICE has not detected the sequence Chirp K-J-K-J-K-J by a time no less than 1.0 ms and no more than 2.5 ms (TWTFS) after completing its own chirp, then the DEVICE is required to revert to the full-speed Default state and wait for the end of Reset. |
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