The human interface device (HID) class includes keyboards, pointing devices, and game controllers. With these devices, the host reads and acts on human input such as keypresses and mouse movements. Hosts must respond quickly enough so users don’t notice a delay between an action and the expected response. Barcode readers can function as HID keyboards with the barcode data emulating keypresses. Other devices with HID interfaces include uninterruptible power supply (UPS) units and display monitors that use HID for user configuration.
Some devices that perform vendor-specific functions can also use the HID class. All HID data travels in reports, which are structures with defined formats.Usage tags in a report tell the host or device how to use received data. For example,a Usage Page value of 09h indicates a button, and a Usage ID value tells which button, if any, was pressed. Windows and other operating systems have included HID drivers since the earliest editions with USB support. For this reason, the HID class has been popular for devices with a variety of vendor-specific functions. A HID can exchange data for any purpose but can use only control and interrupt transfers. Later chapters have more about using HIDs for vendor-specific functions.
Tags: (UPS), Power, structure, Supply, Uninterruptible
