PC Hardware A Beginner’s Guide

(^458) PC Hardware: A Beginner’s Guide

Keyboard Technology

The function of the keyboard is to translate the movement of the user’s fingers into text

characters that are sent to the PC. It may seem like a fairly simple action—you press the

letterAand anAappears on the screen—but there is a lot of activity that takes place to

accomplish this simple feat.

Keys

At the center of keyboard’s function is the keyswitch. When a key is pressed, it closes a

keyswitch and creates a change in the electricity of the keyboard. Each key on the key-

board is a combination of a keyca pand a keyswitch. The keyca p provides a comfortable

surface for your fingers to press and the keyswitch registers the pressure on the key.

Different keyboards can give a different feel to the user, which is caused by a variety

of characteristics of the keys used in the keyboard. These characteristics, which include

travel, tactile feedback, audible signal, and activation pressure, combine to provide the

feelofthekeyboard.Howfarthekeytravelsdownandhowhardthekeymustbepressed

to activate it can both affect the user’s speed. Some users prefer a key that provides a

touch “click” when the key is pressed and some prefer an audible click.

When a key is pressed, the keyswitch is pressed down and signals the keyboard that a

key has been struck. The location of the key must be translated into a code that the

computer recognizes and can translate into the appropriate value. The value associated

with the key is then stored in the PC’s keyboard buffer and eventually passed to the

application with which the user is working.

Hereisasimplificationoftheeventsthatoccurwhenyoupressakeyonthekeyboard:

1. Inside the keyboard is a processor that scans a grid to which all of the
   keyboard’s keys are attached. When a key is pressed, the keyswitch makes
   contact with the keyboard grid, which is detected by the keyboard processor.
   The processor then determines a scan code for the key based on its position on
   the grid. The scan code assigned to the key represents only its position on the
   grid and not the character printed on its key cap.


2. The keyboard processor then sends the scan code to the keyboard interface on
   the PC’s motherboard. This process is also referred to as clocking because the
   scan code is sent as serial data over the data line of the keyboard cable at the
   same time that clock signals are sent over the clock line of the cable.


3. After the keyboard interface has received the keystroke data, it issues a signal
   to IRQ 1 (the IRQ reserved for the keyboard interface), which starts the
   keyboard service routine. The keyboard service routine uses the keyboard