Specifications

V850E2/MN4 USB CDC (Communication Device Class) Driver
R01AN0010EJ0101 Rev.1.01 Page 13 of 117
Feb 01, 2012
3.5 Descriptors
In the USB specification, a set of information that is specific to a function device and is encoded in a predetermined
format is called a descriptor. Each function device sends its descriptor in response to a request from the host device.
3.5.1 Types
The following five types of descriptors are defined:
• Device descriptor
This descriptor is present in all types of devices. It contains basic information such as the version of the supported
USB specification, device class, protocol, maximum packet length available for transfer to Endpoint0, vendor ID,
and product ID.
The descriptor must be sent in response to a GET_DESCRIPTOR_Device request.
• Configuration descriptor
Every device has one or more configuration descriptors. It contains such information as device attributes (power
supplying method) and power consumption. The descriptor must be sent in response to a
GET_DESCRIPTOR_Configuration request.
• Interface descriptor
This descriptor is necessary for each interface. It contains an interface ID, interface class, and the number of
endpoints that are supported. The descriptor must be sent in response to a GET_DESCRIPTOR_Configuration
request.
• Endpoint descriptor
This descriptor is necessary for each endpoint that is specified in the interface descriptor. It defines the transfer type
(direction of transfer), maximum packet length available for transfer to the endpoint, and transfer interval.
Endpoint0, however, does not have this descriptor.
The descriptor must be sent in response to a GET_DESCRIPTOR_Configuration request.
• String descriptor
This descriptor contains an arbitrary string. The descriptor must be sent in response to a
GET_DESCRIPTOR_String request.