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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 ...
It allows for reassignment of some buttons and keys, as well as recording macros and additional functionality like a screen magnifier, and pointer precision enhancer (DPI changer). Microsoft Mouse and Keyboard Center supports USB and Bluetooth devices; it does not support (automatically detect and configure) PS/2 and some older USB devices, [ 1 ...
The most commonly encountered are the "XT" ("set 1") scancodes, based on the 83-key keyboard used by the IBM PC XT and earlier. These mostly consist of a single byte; the low 7 bits identify the key, and the most significant bit is clear for a key press or set for a key release. Some additional keys have an E0 (or rarely, E1 or E2) prefix.
When data from the keyboard arrives, the controller raises an interrupt (a keyboard interrupt) to allow the CPU to handle the input. If a keyboard is a separate peripheral system unit (such as in most modern desktop computers ), the keyboard controller is not directly attached to the keys, but receives scancodes from a microcontroller embedded ...
Some optical keyboards use a special key structure that blocks the light in a certain pattern, allowing only one beam per row of keys (most commonly a horizontal beam). The mechanism of the optical keyboard is very simple – a light beam is sent from the emitter to the receiving sensor, and the actuated key blocks, reflects , refracts or ...
A keyboard matrix circuit is a design used in most electronic musical keyboards and computer keyboards in which the key switches are connected by a grid of wires, similar to a diode matrix. For example, 16 wires arranged in 8 rows and 8 columns can connect 64 keys—sufficient for a full five octaves of range (61 notes).
But when three keys are pressed (electrically closed) at the same time in a "direct contact" keyswitch matrix that doesn't have isolation diodes, the keyboard electronics can see a fourth "phantom" key which is the intersection of the X and Y lines of the three keys. Some types of keyboard circuitry will register a maximum number of keys at one ...
8 leads can detect many more keys if tri-state multiplexing (Figure 1, right) is used instead, which enables (n-1) × (n/2) keys to be detected with just n I/O lines. 8 I/O can detect 28 individual keys without ambiguity. Issues can occur with some combinations if two keys are pressed simultaneously.