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USB Class Codes

March 2, 2006

USB defines class code information that is used to identify a device’s functionality and to nominally load a device driver based on that functionality. The information is contained in three bytes with the names Base Class, SubClass, and Protocol. (Note that ‘Base Class’ is used in this description to identify the first byte of the Class Code triple. That terminology is not used in the USB Specification). There are two places on a device where class code information can be placed.One place is in the Device Descriptor, and the other is in Interface Descriptors. Some defined class codes are allowed to be used only in a Device Descriptor, others can be used in both Device and Interface Descriptors, and some can only be used in Interface Descriptors. The table below shows the currently defined set of Base Class values, what the generic usage is, and where that Base Class can be used (either Device or Interface Descriptors or both).

Base Class	Descriptor Usage	Description
00h	Device	Use class information in the Interface Descriptors
01h	Interface	Audio
02h	Both	Communications and CDC Control
03h	Interface	HID (Human Interface Device)
05h	Interface	Physical
06h	Interface	Image
07h	Interface	Printer
08h	Interface	Mass Storage
09h	Device	Hub
0Ah	Interface	CDC-Data
0Bh	Interface	Smart Card
0Dh	Interface	Content Security
0Eh	Interface	Video
0Fh	Interface	Personal Healthcare
DCh	Both	Diagnostic Device
E0h	Interface	Wireless Controller
EFh	Both	Miscellaneous
FEh	Interface	Application Specific
FFh	Both	Vendor Specific

Base Class 00h (Device)

This base class is defined to be used in Device Descriptors to indicate that class information should be determined from the Interface Descriptors in the device. There is one class code definition in this base class. All other values are reserved.

This value is also used in Interface Descriptors to indicate a null class code triple.

Base Class	SubClass	Protocol	Meaning
00h	00h	00h	Use class code info from Interface Descriptors

Base Class 01h (Audio)

This base class is defined for Audio capable devices that conform to the Audio Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values. Values outside of that defined spec are reserved. These class codes may only be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
01h	xxh	xxh	Audio device

Base Class 02h (Communications and CDC Control)

This base class is defined for devices that conform to the Communications Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values. Values outside of that defined spec are reserved. Note that the Communication Device Class spec requires some class code values (triples) to be used in Device Descriptors and some to be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
02h	xxh	xxh	Communication device class

Base Class 03h (HID – Human Interface Device)

This base class is defined for devices that conform to the HID Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values. Values outside of that defined spec are reserved. These class codes can only be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
03h	xxh	xxh	HID device class

Base Class 05h (Physical)

This base class is defined for devices that conform to the Physical Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values. Values outside of that defined spec are reserved. These class codes can only be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
05h	xxh	xxh	Physical device class

Base Class 06h (Still Imaging)

This base class is defined for devices that conform to the Imaging Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values. Values outside of that defined spec are reserved.

Base Class	SubClass	Protocol	Meaning
06h	01h	01h	Still Imaging device

Base Class 07h (Printer)

This base class is defined for devices that conform to the Printer Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values. Values outside of that defined spec are reserved. These class codes can only be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
07h	xxh	xxh	Printer device

Base Class 08h (Mass Storage)

This base class is defined for devices that conform to the Mass Storage Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values. Values outside of that defined spec are reserved. These class codes can only be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
08h	xxh	xxh	Mass Storage device

Base Class 09h (Hub)

This base class is defined for devices that are USB hubs and conform to the definition in the USB specification. That specification defines the complete triples as shown below. All other values are reserved. These class codes can only be used in Device Descriptors.

Base Class	SubClass	Protocol	Meaning
09h	00h	00h	Full speed Hub
		01h	Hi-speed hub with single TT
		02h	Hi-speed hub with multiple TTs

Base Class 0Ah (CDC-Data)

This base class is defined for devices that conform to the Communications Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values.Values outside of that defined spec are reserved. These class codes can only be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
0Ah	xxh	xxh	CDC data device

Base Class 0Bh (Smart Card)

This base class is defined for devices that conform to the Smart Card Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values.Values outside of that defined spec are reserved. These class codes can only be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
0Bh	xxh	xxh	Smart Card device

Base Class 0Dh (Content Security)

This base class is defined for devices that conform to the Content Security Device Class Specification found on the USB-IF website. That specification defines the usable set of SubClass and Protocol values. Values outside of that defined spec are reserved. These class codes can only be used in Interface Descriptors.

Base Class	SubClass	Protocol	Meaning
0Dh