USB2.0的电气标准，可以用于学习USB2.0相关知识，了解相关的标准协议3.2 Transmitting
EL 2 A USB 2.0 high-speed transmitter data rate must be 480 Mb/s +-0.05%
Reference documents: USB 2.0 Specification, Section 7. 1.11
Test descr iption: Section 4.1
eL 3 A USB 2.0 downstream facin
