USB Device speed identification

Full-speed device cable and resistor


Low-speed device cable and resistor

• By position of the pull-up resister on device, if on D-, => use low-speed mode
  
• if on D+, then the device is full-speed or high-speed
  
  • hub drive SE0
    
  • device detects assertion of SE0
    
    • if nothing happened, then it is a full-speed device
    • if device send ChirpK, then hub send K-J Chirp pairs, and device detects it successfully, => use high-speed mode
      
      • any fails => use full-speed mode

Chirp J/K

低速下空闲状态为“K”状态；
全速下空闲状态为“J”状态；
高速下空闲状态为“SE0”状态；

	DP	DM
HS-J	1	0
HS-K	0	1
FS-J	1	0
FS-K	0	1
LS-J	0	1
LS-K	1	0

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USB specification revision 2.0, 7.1.5 device speed identification

USB2.0速度识别
http://hi.baidu.com/doyanger/blog/item/af45d995dd64f419d31b704d.html

[硬件和PCB]usb高速握手过程
http://www.52rd.com/Blog/Detail_RD.Blog_swordlife_17644.html

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HS SOF