USB : Overview    USB Is Like A Railroad  

The USB name for the process of submitting our specs is called “Enumeration.” You can see from our analogy above that when the device is plugged in to the USB cable, it must submit a bunch of numerical tables called Descriptors that tell the PC everything about the device and the data that it will send in each direction.

If the device sends descriptors that the PC thinks are correctly formed, and if the PC decides that there is enough bandwidth available on the USB cable for this device, then the PC will allow the device to send and receive data over the USB. If any mistakes have been made in constructing or sending these Descriptors, then the PC will simply ignore the device, and give no indication why.


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