USB3.0和USB3.1技术已稳定成熟，但基于某些条件，USB2.0仍起到重要的作用。确保产品通过USB-IF规定的USB.2.0一致性测试仍被广泛关注，本文介绍了美国Lecroy公司Qualiphy软件对USB2.0产品的一致性部分项目的测试，并结合USB-IF规范和USB2.0协议对波形进行简要分析。

一．测试项目：1.EL_<2,4,6,7> Signal Quality Overall Result

EL_2:A USB2.0high-speed transmitter data rate must be 480Mb/s±0.05%.

EL_4:A USB2.0upstream facing port on a device without a captive cable must meet Template 1 transformwaveform requirements measured at TP3.

EL_6:A USB2.0 HSdriver must have 10% to 90% differential rise and fall times of greater than500 ps.

EL_7:A USB2.0 HSdriver must have mounotonic data transitions over the vertical openingsspecified in the appropriate eye pattern template.

2.EL_<28,29,31> HS Chirp Timing

 

EL_29:The chirphandshake generated by a device must be at least 1ms and not more than 7 ms induration.

 

EL_31: During thespeed detection,when a device detects a valid Chirp K-J-K-J-K-J sequence,thedevice must disconnect its 1.5K resistor and enable its high-speed terminationswithin 500us.

3EL_<27,28,38-40>HS Suspend Resume Reset

EL_38:A devicemust revert to full-speed termination no later than 125us after there is a 3msidle period on the bus.

Devices begin thetransition to the Suspend state after they see a constant Idle state on theirupstream facing buslines for more than 3.0 ms. From the perspective of a deviceoperating in high-speed mode, a Reset and a Suspend are initiallyindistinguishable, so the first part of the device response is the same as fora Reset. When a device operating in high-speed mode detects that the data lineshave been in the high-speed Idle state for at least 3.0 ms, it must revert tothe full-speed configuration no later than 3.125 ms (TWTREV) after the start ofthe idle state. Reversion to full-speed is accomplished by disconnecting itstermination resistors and reconnecting its D+ pull-up resistor.No earlier than100 μs and no later than 875 μs (TWTRSTHS) after reverting to full-speed, thedevice must sample the state of the line. If the state is a full-speed J, thedevice continues with the Suspend process.

Referencedocuments:USB2.0 Specification,Section 7.1.7.6

EL_27: Device musttransmit a chirp handshake no sooner than 3.1ms and no later than 6.0ms whenbeing reset form a non-suspended high-speed mode.The timing is measured fromthe begining of the last uSOF transmitted before the reset begin.