Hello, brother Shui wants to talk about USB with you today. The little friend next to him immediately jumped up, “what?! USB, such an old topic, are you serious?”



Reply from brother Shui:



It’s hard to find a bosom friend for a man with such connotation as brother Shui! No more nonsense. Let’s talk about the history of USB. You know, brother Shui is very knowledgeable and loves to share. To tell the truth, I’m in a panic if I don’t pour it out~



Here we go!



USB was first proposed by Intel in conjunction with several companies and launched in 1996 to achieve hot plug and plug and play as much as possible. It is much faster than parallel ports (such as EPP, LPT) and serial ports (such as RS-232). The first generation USB, named low speed USB, with a transmission speed of about 1.5mbps, did not attract much attention at that time. However, with the improvement from generation to generation, after more than 20 years of development, USB has almost become a standard interface.



Let’s take a look at the comparison of theoretical speed and feel the shock of science and technology!



Of course, now usb-if has released the latest specifications, changing USB3.0 and usb3.1 gen1/2 to USB3.0 Gen 1, usb3.2 Gen2, usb3.2 gen2x2, and its own official names: super speed USB, super speed USB 10Gbps, super speed USB 20gbps.



Seeing so many names, most people should be so confused. Even a man like brother Shui has to pause for 2 seconds. The skill points of the merchant are all about deception~



Back to the point, brother Shui does tests, so I still want to show and share test skills with you. USB2.0 adopts the method of half duplex communication, with only one pair of differential lines to transmit and receive data; For high-speed signal transmission, USB3.0 adopts full duplex communication method, and two pairs of high-speed differential lines are used to transmit data and receive data. Therefore, different test specifications lead to different test schemes.



USB2.0 physical layer consistency test



The highest bit rate of USB2.0 is 480mbps, which is a differential signal with frequency of 240mhz and amplitude of 0~400mv. Therefore, during the test, higher requirements are put forward for the oscilloscope bandwidth, which requires more than 2G bandwidth. A list should be prepared:



Ÿ 1 set of oscilloscope with bandwidth above 2G



Ÿ 1 set of 1.8g bandwidth probe



Ÿ 1 set of official fixture



Ÿ 1 set of USB2.0 test software



See video 1:usb2.0 device physical layer consistency test and video 2:usb2.0 host physical layer consistency test for video explanation.



USB3.0 physical layer consistency test



The highest bit rate of USB3.0 is 5Gbps, which is almost 10 times that of USB2.0. Therefore, it requires an oscilloscope bandwidth of more than 12.5gh. In addition, there are two types of USB3.0 interfaces, typea and typec, which should be noted during testing. The detailed list is as follows:



Ÿ 1 set of oscilloscope above 12.5ghz



Ÿ 1 set of USB 3.0 clamps (typea, typec)



Ÿ 3 SMA cables



Ÿ 1 signal generator



Ÿ 1 set of USB3.0 test software



See video 3:3.0 txdevice physical layer consistency test and video 4:3.0 txhost physical layer consistency test for video explanation.



Operation steps:



1 connect the tested part and oscilloscope



2 select the corresponding test software on the oscilloscope and set the parameters



3 click test and wait for results



In general, the built-in special test software of the oscilloscope is already very intelligent. As long as you follow the steps, you can go through it once. The key lies in the preparatory work, especially the hardware must meet the requirements.

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