[ The PC Guide | Systems and Components Reference Guide | Keyboards
| Keyboard Construction and Operation | Other
Regular Keyboard Components ]
LED Indicators
Almost all keyboards come with a set of three LED (light-emitting diode) indicator lights. These
are used to demonstrate to the user the current state of the keyboard's operation. The
usual indicators are:
- Num Lock: Indicates when the numeric keypad is enabled. When lit, the numeric
keypad of course generates numbers; when not lit, the other function of those keys (cursor
control) is activated.
- Caps Lock: Pretty self-explanatory.
- Scroll Lock: Indicates when the Scroll Lock function has been enabled. This
causes certain programs to behave differently when cursor keys are used. For example, when
Scroll Lock is enabled, pressing the down arrow in Microsoft Excel causes the entire
worksheet to scroll down one row instead of moving the focus point down one cell as the
down arrow normally would.
|
The three standard LEDs found on most typical
keyboards. |
These indicators are of course changed by pressing the keys on the keyboard, which
share their names. (For more information on each of these "lock" functions, see the discussion of the keyboard's modification keys.)
However, the keyboard is not really "in charge" of them. The keyboard tells the
system when the appropriate key is pressed to enable or disable one of these modes, and
the system controls the LED's status in response. This may seem an unnecessarily indirect
way of doing things, but it has an important advantage: there is no chance of the system
and the keyboard getting "out of sync". The indicators always correctly the
system's mode. This capability also allows the system to set the
state of the Num Lock LED when the PC is started, if desired.
Some keyboards include additional LED indicators. For example, programmable keyboards
may have an LED to show when programming features are activated. The LEDs all function in
pretty much the same way, and problems with these indicators are very unusual.
 Next: Keyboard
Operation
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