K e y b o a r d  

CPT 105 · Franklin College · Erich Prisner · 2002-2007

On the surface

Most common: 104 key Windows keyboard.

Notebooks have fewer keys (mine has 84)---usually no numeric keypad.
Apple keyboards fewer keys as well
Variety of other keyboards available.


Switches, connected to a microprocessor, one for each key.
Key "bridges" circuit
microprocessor observes these circuits and compares to "character map", also for combinations
Computer also has a character map
typematics: press key longer: what happens?

"Typewriter" mechanics

provides "feel" of a typewriter. Clicks, keys jump back, ...

Into the cable ...

small amount of power comes from the computer to the keyboard
letter information is sent from the keyboard to the computer.
Sent is a string of 0s and 1s.
Characters are encoded as Bytes

Bits and Bytes I

Everything in computers is encoded as 1s or 0s, either through the cable or in storage.
Bit: either a "0" or a "1".
Byte: A package of 8 bits.
How many thing can you encode using 8 bits?
(Extended) Ascii code: Encoding of characters using a byte (sequence of 8 bits). For instance "A" is encoded as "65", "a" as "97".

Erich Prisner, August 2003