[ The PC Guide | Systems and Components Reference Guide | Keyboards
| Keyboard Construction and Operation | Other
Regular Keyboard Components ]
Internal Keyboard Circuitry
The "brain" of the keyboard is the circuitry within the unit that handles the
processing of keystrokes and exchanging information with the host system (the rest of the
PC). While keyboards are fairly simple devices, you might be surprised at just how complex
the internal circuitry is in a keyboard. In some ways it's like another whole computer in
there...
In fact, the keyboard has within it small versions of several components you find
within the PC as a whole. It has its own microprocessor, which "runs the show"
so to speak. (This is of course a tiny CPU like the 8048, not a full-fledged CPU as the main PC hardware uses.) There is
also some read-only memory (ROM) that runs this
small processor, similar to the system BIOS code
on the motherboard. Programmable keyboards also contain some EEPROM memory to hold
programming information; this functions as if it were a tiny hard disk, in a way. Sort of.
;^)
|
Internal circuit board from a typical keyboard. The
chip is the
keyboard controller. Note the LEDs sticking up from the circuit
board, in this design; they "poke through" holes in the keyboard case. |
This internal circuitry has two fundamental jobs. First, it is responsible for sensing
the raw signals created by the keyswitches as they make electrical contact, and
translating them into signals that can be sent to the PC. Due to the electrical
characteristics of keystrokes, this is not as simple as it sounds. Second, it handles the
actual interfacing between the keyboard and the rest of the PC system. The interface
between the PC and the keyboard is a full bi-directional serial communications line, with
its own special protocols and commands.
The operation of the internal keyboard circuitry is discussed in more detail in the section that describes the operation of the keyboard, including
keypress detection and scan code generation, interfacing, and signaling.
 Next: Keyboard Cable
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