USB Descriptors can tell the host computer what the USB device is and how to
communicate.
Device Descriptors
At the top level, the Device Descriptor contains the base information of the USB
device including but not limited to:
USB Version
Device level class, subclass
and protocol
Vendor and Product ID (VID
and PID)
Manufacturer, product and
serial number
The number of different
configurations the device has
Configuration Descriptors
The Configuration Descriptor contains the setup for a specific configuration
containing:
Size of the
configuration
Number of interfaces
Power attributes
A USB device can contain multiple configurations and switch between them, for
example, a configuration for the bootloader and another for the actual
application.
Interface Descriptors
USB interface descriptors define a specific interface within a USB configuration,
detailing its purpose and functionality, including:
Alternative settings
Number of Endpoints
Interface class, subclass and protocol
Endpoint Descriptors
USB endpoint descriptors specify the attributes of a particular endpoint within an
interface, such as:
Endpoint address
Direction (IN/OUT)
Type (control, isochronous, bulk or interrupt)
Packet size
Polling interval
USB Descriptor Tree
The figure below shows how the different descriptors (described above) combined into
a working device can be visualized in the USB descriptor tree.
Functional Descriptors
Unlike standard descriptors that convey basic device information, functional
descriptors can define additional attributes related to specific device classes or
functionality. For the CDC, this is done for the communication interface and can
contain information on interface grouping or what parts of a model defined in the
Subclass field are implemented on the device.
The online versions of the documents are provided as a courtesy. Verify all content and data in the device’s PDF documentation found on the device product page.
