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Section 4. USB Communications
COMMANDS
Command requests and responses are sent to and received from the device using feature reports. Command requests are sent to the device using the HID class specific request Set_Report. The response to a command is retrieved from the device using the HID class specific request Get_Report. These requests are sent over the default control pipe. When a command request is sent, the device will Nak the Status stage of the Set_Report request until the command is completed. This insures that as soon as the Set_Report request is completed, the Get_Report request can be sent to get the command response. The usage ID for the command message was shown previously in the Usage Table.
The following table shows how the feature report is structured for command requests:
Offset
0
1
2 – 23
Field Name
Command Number
Data Length
Data
The following table shows how the feature report is structured for command responses.
Offset
0
1
2 – 23
Field Name
Result Code
Data Length
Data
COMMAND NUMBER
This
Value | Command Number | Description |
0 | GET_PROPERTY | Gets a property from the device |
1 | SET_PROPERTY | Sets a property in the device |
DATA LENGTH
This
DATA
This
13