HID Sensor Usage Tables - USB.org

66 HID Sensor Usages
Each Named Array takes on only one value (“radio button” style), so Report Count must be 1;
Input Report Item or Feature Report Item must have “Array” flag (use Const_Arr_Abs or
Data_Arr_Abs).
See Also
For more information about HID Selectors; please refer to Section 3.4.2.1, 3.4.3.1, and A.4 of the USB HID
Usage Tables specification (Reference Document [3]).
3.8 HID Usage Page
All HID Usages for sensors are defined to occur on HID Usage Page 0x20.
3.9 HID Units
Usages have by definition a default Unit of Measure, which will be mentioned in the Usages Table.
For example, a Thermometer sensor may have a Data Field (Input Report Item) Usage called “Current
Temperature”, and its default Unit of Measure may be “Degrees Celsius”.
If not explicitly overridden, the programmer should assume the default Unit of Measure.
It is possible to override the default Unit of Measure by explicitly including a Unit() descriptor item in
the HID Report Descriptor. For example, “Degrees Celsius” could be overridden by declaring
Unit(Kelvin).
See Also
For more information about HID Units; please refer to Sections 6.2.2.7 of the Device Class Definition for
Human Interface Devices specification (Reference Document [2]).
Usages state specifically whether Units are required to define a time base or other reference. A Units
requirement implies the definition or Units, Physical Maximum, Physical Minimum and Unit Exponent
descriptor items.
Units are global items that persist from main item to main item. Units can be disabled by setting Units to
“None”, and Physical Maximum, Physical Minimum and Unit Exponent equal to 0.
Normalized Usages use Logical Minimum and Logical Maximum to define their range of values. These
values are automatically scaled by an application to fit the range of values required for the target operation
and do not require Units. This is useful where, for example, the Usage is expressed as a Percent; use a
Logical Minimum of 0 and a Logical Maximum of 100.
To declare a vector (Vx, Vy, or Vz) as a linear velocity or acceleration, define the System field of the Unit
item associated with the vector usage to be either SI Linear (1) or English Linear (3). To declare vectors as
angular velocity or acceleration, define the System field of the Unit item to be either SI Rotation (2) or
English Rotation (4).