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The PC 97 standard requires that a computer's BIOS must detect and work with USB HID class keyboards that are designed to be used during the boot process. Some keyboards implement the USB Boot Keyboard profile specified in the USB Device Class Definition for Human Interface Devices (HID) v1.11 and are explicitly configured to use the boot protocol.
Key rollover is the ability of a computer keyboard to correctly handle several simultaneous keystrokes. A keyboard with n-key rollover (NKRO) can correctly detect input from each key on the keyboard at the same time, regardless of how many other keys are also being pressed. Keyboards that lack full rollover will register an incorrect keystroke ...
However, the USB boot keyboard class (designed to allow the BIOS to easily provide a keyboard in the absence of OS USB HID support) only allows 6-key rollover. Some keyboard peripherals support only the latter class, and some OSes may fail to switch to using the full HID keyboard class with a device after boot. [14]
Such devices can use an external power supply, which is allowed by the standard, or use a dual-input USB cable, one input of which is for power and data transfer, the other solely for power, which makes the device a non-standard USB device. Some USB ports and external hubs can, in practice, supply more power to USB devices than required by the ...
A computer keyboard is a built-in or peripheral input device modeled after the typewriter keyboard [1] [2] which uses an arrangement of buttons or keys to act as mechanical levers or electronic switches.
PS/2 did not typically support plug-and-play, which means that connecting a PS/2 keyboard or mouse with the computer powered on does not always work and may pose a hazard to the computer's motherboard. Likewise, the PS/2 standard did not support the HID protocol. The USB human interface device class describes a USB HID.
ADDR: Address of USB device (maximum of 127 devices). ENDP: Select endpoint hardware source/sink buffer on device. (E.g. PID OUT would be for sending data from host source buffer into the USB device sink buffer.) By default, all USB devices must at least support endpoint buffer 0 (EP0).
This section describes the power distribution model of USB that existed before Power-Delivery (USB-PD). On devices that do not use PD, USB provides up to 4.5 W through Type-A and Type-B connectors, and up to 15 W through USB-C. All pre-PD USB power is provided at 5 V. For a host providing power to devices, USB has a concept of the unit load ...