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What is a Keyboard Controller?

written by: •edited by: Bill Fulks•updated: 12/9/2010

How does your keyboard communicate with your computer? There's more to it than a lump of plastic, springs and a cable - the keyboard controller is quietly managing every keystroke you send to your PC.

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    What is a Keyboard Controller?

    motherboard keyboard controller looks after all keyboards If you thought that typing a few characters into your PC keyboard automatically sent them into your computer, you would be wrong – there is a lot happening in the background, thanks to the keyboard controller.

    Whether you use a serial connector, PS/2 connector or USB keyboard, the entry of text, numbers and characters is managed by the motherboard keyboard controller, a component that allows human interaction with a computer. As with many motherboard components, if damaged the prone keyboard controller will render your PC largely unusable.

    This motherboard-mounted chip is probably the single most important human interface component in any modern computer. The first (hobbyist) home computers shipped without any form of human interface – instead they used switches and connectors – and the keyboard controller is a component whose origins lay in the early days of the digital revolution in the late 1960's.

    (Image via hp.com)

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    What Does the Motherboard Keyboard Controller Do?

    The motherboard keyboard controller explained Put simply, the keyboard controller translates the keystrokes on your keyboard into the characters that appear on screen, or applies them as the commands that allow you to open desktop menus from your keyboard.

    When a key is pressed on your keyboard, an electrical pulse is sent to the computer via your cable or wireless connection. This is then sent from the PS/2 or USB port to the keyboard controller where it then signals the CPU (the computer’s processor) to allow the entry of the text or keyboard command.

    The keyboard controller is also responsible for activating LED's on the keyboard such as Caps Lock; this will not illuminate without an instruction from the keyboard controller, which in turn requires confirmation from the operating system that entered text will be in upper case when Caps Lock is pressed.

    (Image via wikipedia.org)

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    Where is the Motherboard Keyboard Controller?

    Depending on your motherboard, you can find the keyboard controller in different places, but most commonly it is found near the PS/2 or USB connector that is intended for your keyboard.

    Usually this connector will sit over the top of the keyboard controller chip which will make it difficult to identify, as the plastic insulation block of your USB or PS/2 connector typically sits around a centimeter over the motherboard.

    However replacement of this component is both difficult and largely pointless. Unless you have identical motherboards, of which one is used for spares, acquiring a single compatible keyboard controller will be difficult as such integrated circuits are usually purchased in bulk. Furthermore, unless you are a particularly skilled engineer removing the back panel and replacing the keyboard controller will take some time to get right.

    The preferred method of replacement is not to swap out the component but to utilise an entirely new motherboard which while expensive will save a lot of problems.