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USB General Operation

Descriptors

USB devices report their attributes using descriptors. A descriptor is a data structure with a defined format, which begins with

a byte-wide field that contains the total number of bytes in the descriptor followed by a byte-wide field that identifies the

descriptor type.

Class and vendor specific descriptors may be returned in one of two ways. Class and vendor specific descriptors that are

related to standard descriptors are returned in the same data buffer as the standard descriptor. If a class or vendor specific

descriptor is not related to a standard descriptor, it is returned using class or vendor specific requests.

Device Descriptor

A device descriptor describes general information about a USB device, which applies globally to the device and all of the

device’s configurations (see Table 3). A USB device has only one device descriptor. Vendor ID, Product ID, and Device

Release Number can be changed. The Manufacturer Name, Product Name, and Serial Number can also be customized.