Keyboard controller (computing)

Article summary

-Mainboard In computing, a keyboard controller is a device that interfaces a keyboard to a computer. Its main function is to inform the computer when a key is pressed or released. 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 in the keyboard via some kind of serial interface. In this case, the controller usually also controls the keyboard's LEDs by sending data back to keyboard through the wire. The IBM PC AT used an Intel 8042 chip to interface to the keyboard. This chip had two additional functions: it controlled access to the Intel 80286 CPU's A20 line in order to implement a workaround for a chip bug, and it was used to initiate a software CPU reset in order to allow the CPU to transition from protected mode to real mode because the 286 did not allow the CPU to go from protected mode to real mode unless the CPU is reset. The latter was a problem because the BIOS and services provided by real mode operating systems such as MS-DOS and similar operating systems could only be called by programs in real mode.…

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