An array provides an alternate means for describing the data returned from a group of buttons. Arrays are more efficient, if less flexible than variable items. Rather than returning a single bit for each button in the group, an array returns an index in each field that corresponds to the pressed button (like keyboard scan codes). An out-of range value in and array field is considered no controls asserted. Buttons or keys in an array that are simultaneously pressed need to be reported in multiple fields. Therefore, the number of fields in an array input item (Report Count) dictates the maximum number of simultaneous controls that can be reported. A keyboard could report up to three simultaneous keys using an array with three 8-bit fields (Report Size = 8, Report Count = 3). Logical Minimum specifies the lowest index value returned by the array and Logical Maximum specifies the largest. The number of elements in the array can be deduced by examining the difference between Logical Minimum and Logical Maximum (number of elements = Logical Maximum - Logical Minimum + 1).
Indicates that the control emits a fixed-sizestream of bytes. The contents of the data field are determined by the application. The contents of the buffer are not interpreted as a single numeric quantity. Report data defined by a Buffered Bytes item must be aligned on an 8-bit boundary. The data from a bar code reader is an example.
Indicates that the control emits a fixed-sizestream of bytes. The contents of the data field are determined by the application. The contents of the buffer are not interpreted as a single numeric quantity. Report data defined by a Buffered Bytes item must be aligned on an 8-bit boundary. The data from a bar code reader is an example.
Constant indicates the item is a static read-only field in a report and cannot be modified (written) by the host.
Data indicates the item is defining report fields that contain modifiable device data
Indicates whether the raw data from the device has been processed in some way, and no longer represents a linear relationship between what is measured and the data that is reported. Acceleration curves and joystick dead zones are examples of this kind of data. Sensitivity settings would affect the Units item, but the data would still be linear.
Indicates whether the control has a state in which it is not sending meaningful data. One possible use of the null state is for controls that require the user to physically interact with the control in order for it to report useful data. For example, some joysticks have a multidirectional switch (a hat switch). When a hat switch is not being pressed it is in a null state. When in a null state, the control will report a value outside of the specified Logical Minimum and Logical Maximum (the most negative value, such as -128 for an 8-bit value).
Indicates whether the control has a preferred state to which it will return when the user is not physically interacting with the control. Push buttons (as opposed to toggle buttons) and selfcentering joysticks are examples.
Indicates whether the data “rolls over” when reaching either the extreme high or low value. For example, a dial that can spin freely 360 degrees might output values from 0 to 10. If Wrap is indicated, the next value reported after passing the 10 position in the increasing direction would be 0.
Indicates whether the raw data from the device has been processed in some way, and no longer represents a linear relationship between what is measured and the data that is reported. Acceleration curves and joystick dead zones are examples of this kind of data. Sensitivity settings would affect the Units item, but the data would still be linear.
Indicates whether the Feature or Output control's value should be changed by the host or not. Volatile output can change with or without host interaction. To avoid synchronization problems, volatile controls should be relative whenever possible. If volatile output is absolute, when issuing a Set Report (Output), request set the value of any control you don't want to change to a value outside of the specified Logical Minimum and Logical Maximum (the most negative value, such as -128 for an 8-bit value). Invalid output to a control is ignored by the device
Indicates whether the control has a state in which it is not sending meaningful data. One possible use of the null state is for controls that require the user to physically interact with the control in order for it to report useful data. For example, some joysticks have a multidirectional switch (a hat switch). When a hat switch is not being pressed it is in a null state. When in a null state, the control will report a value outside of the specified Logical Minimum and Logical Maximum (the most negative value, such as -128 for an 8-bit value).
Indicates whether the control has a preferred state to which it will return when the user is not physically interacting with the control. Push buttons (as opposed to toggle buttons) and selfcentering joysticks are examples.
Indicates whether the data is absolute (based on a fixed origin) or relative (indicating the change in value from the last report). Mouse devices usually provide relative data, while tablets usually provide absolute data.
In variable fields, each field represents data from a physical control. The number of bits reserved for each field is determined by preceding Report Size/Report Count items. For example, a bank of eight on/off switches could be reported in 1 byte declared by a variable Input item where each bit represents one switch, on (1) or off (0) (Report Size = 1, Report Count = 8). Alternatively, a variable Input item could add 1 report byte used to represent the state of four threeposition buttons, where the state of each button is represented by two bits (Report Size = 2, Report Count = 4). Or 1 byte from a variable Input item could represent the x position of a joystick (Report Size = 8, Report Count = 1).
Indicates whether the Feature or Output control's value should be changed by the host or not. Volatile output can change with or without host interaction. To avoid synchronization problems, volatile controls should be relative whenever possible. If volatile output is absolute, when issuing a Set Report (Output), request set the value of any control you don't want to change to a value outside of the specified Logical Minimum and Logical Maximum (the most negative value, such as -128 for an 8-bit value). Invalid output to a control is ignored by the device
Indicates whether the data “rolls over” when reaching either the extreme high or low value. For example, a dial that can spin freely 360 degrees might output values from 0 to 10. If Wrap is indicated, the next value reported after passing the 10 position in the increasing direction would be 0.
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Indicates whether the data is absolute (based on a fixed origin) or relative (indicating the change in value from the last report). Mouse devices usually provide relative data, while tablets usually provide absolute data.