HID Usage Tables Document 1.1 - C. Scott Ananian

Universal Serial Bus HID Usage Tables 11 IntroductionUsages are part of the HID Report descriptor and supply an application developer with information aboutwhat a control is actually measuring or reporting. In addition, a Usage tag can be used to indicate thevendor’s suggested use for a specific control or group of controls. While most of the items within a Reportdescriptor describe the format of the data—for example, three 8-bit fields—the Usage tags define whatshould be done with the data—for example, x, y, and z input. This feature allows a vendor to ensure that theuser sees consistent function assignments to controls across applications. It is also the key feature withinHID Report descriptors that allows system or application software to know the meaning of data items, orcollections of data items, so the data items can be correctly interpreted or routed to the system or applicationsoftware that consumes them.1.1 ScopeThis document is the most current and complete list of currently defined usages. With the exception of theKeyboard/Keypad Page (0x07), this document is a superset of the usages defined in the USB Device ClassDefinition for Human Interface Devices (HID), also called the HID Specification. Keyboard/Keypad Pageusages are listed in the HID Specification, and are not repeated in this document due to length. Usages forother pages listed in the HID Specification (Generic Desktop, LED, and Button pages) are repeated in thisdocument with additional information. In case of a discrepancy, this document takes precedence over theHID Specification for those usages.Usage definitions for Monitor, Power, Bar Code Scanner, and Point of Sale devices are in process as of thispublication date and are not covered in this document. For details about those usages, see the device classspecifications for those devices.1.2 PurposeThis document defines constants that can be interpreted by an application to identify the purpose andmeaning of a data field in a HID report.Usages are also used to define the meaning of groups of related data items. This is accomplished by thehierarchical assignment of usage information to collections. Usages identify the purpose of a collection andthe items it contains. Each Input, Output, Feature, and/or Collection data item within a Collection itemcan be assigned a purpose with its own usage item. Usages assigned to a collection apply to the items withinthe collection.In some cases a usage applied to a collection can redefine the meaning of the usages it contains. An exampleof this is the Usage Selected Indicator on the LED page.Usages are also used to specify the meaning of each element within an Array data item.Version 1.1 April 8, 1999