keyboard

keyboard

The keyboard is the primary input device. (The mouse is also a primary input device but lacks the ability to easily transmit textual information.) The keyboard also contains certain standard function keys, such as the Escape key, tab and cursor movement keys, shift and control keys, and sometimes other manufacturer-customized keys.

The computer keyboard uses the same key arrangement as the mechanical and electronic typewriter keyboards that preceded the computer.

The Main Keys (a,b,c,...) on the keyboard behave like a standard typewriter.

Modifier Keys (Ctrl, Alt): These keys have specific functions in software programs when used in combination with the letter keys. For example, to do Ctrl 'A' you would hold down the modifier key Ctrl and tap the A key once. In general, the Ctrl key on a PC = the Command key on a Mac; the Alt key on a PC = the Option key on a Mac. Macintosh's also have a third Modifier key: Control.

Function Keys: These include the Esc and F1 through F12 keys at the top of the keyboard, as well as the Home, Help, End, Del, Page Up & Down keys located above the arrow keys. Their functions are different depending on the software program that you are running. They can sometimes be programmed.

Arrow Keys: Located in between the number pad and the main keys, the arrows let you move around in most programs.

Number Pad: If the NumLock is on (turn on/off with button in upper left-hand corner of number pad), the number keys give numbers. If it is off, the keys act like the arrow keys (8 is up, 2 is down, etc.).

Indicator Lights: Located above the number pad, they tell you if the NumLock or Caps Lock are on.

Keyboards are used to give inputs in the form of text.

All keyboards have keys for basic cursor movements such as carriage return, delete, page up/down, cursor movement keys etc

Keyboard Types

[1]XT Keyboard

[2]AT Standard

[3]AT Enhands

Working of Keyboard

The keyboard consists of a keyboard controller looking after the scan matrix. The scan matrix is a set of crossing lines. At each crossing, a small switch is located above which a key is present supported by a spring

The key that is pressed is determined by activating the vertical lines and determining from which horizontal line a signal is detected. The key pressed is identified by the vertical and the horizontal line.

Data transfer is serial

Keyboard Buffer

The data from the keyboard is held in the keyboard buffer, which is managed by two pointers - read pointer and write pointer.

The write pointer points to the next location in the buffer onto which data can be written. The read pointer points to the location from where data can be read.