Keyboard

The keyboard is the main means of issuing directions of your PC. A computer keyboard is quite similar to that of typewriter. But it has some additional key. They are :

1) Arrow and other movement key (Home, PgUp, PgDn)
2) Function keys (F1-F10 or F1 to F12
3) Text editing keys (Backspace, del, ins)
4) Modifier keys ( Shift, Ctrl, Alt)
5) Enter key,
6) Other special keys (print screen, Scroll Lock and so on)
7) LED status indicator

Keyboards are of 2 main styles they are:

1) Standard with usually 83-84 key and
2) Enhanced with 101 key or more. In the figure it is the enhance keyboard.

Typewriter keys are the normal keys on the keyboard. These keys includes letters, numbers and punctuation symbols.

Keyboard consists of electronic circuit to decide which key has been pressed. Thus the keyboard control electronic circuit has to perform the following functions :

a) Sensing a key pressed.
b) Encode the sensed key
c) Send the encoded data to computer.

When a key on a keyboard is pressed, the corresponding key switch is activated. They keyboard electronic circuit make use of matrix scanning technique in order to determine which key has been pressed. Then a standard 8-bit binary code is generated to correspond to the depressed key value. This 9-bit scan code is sent into the computer as input data.

The keyboard control electronics circuitry not only just senses the pressed key but it also keep track that when the operator or user releases that key. There are separate scan codes for the press and release of each key, so that they can be identified very easily. Each separate key action is recorded by the keyboard control electronic circuit and send to the computer as distinct scan code. The scan codes are communicated to the pressing unit via interrupt mechanism.

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