How are keys pressed on a keyboard interpreted correctly by the computer? (How does a keyboard communicate with the CPU?)

                                           Keyboard is the main and the most commonly used input device of the computer. Keyboard came into use, after the decline of punch cards. Since then, it has been identified as an essential feature of the computer. Generally, a keyboard is a board with an arrangement of buttons or keys acting as electronic switches. Now, let’s see how the Keyboard works.

                                              Typical QWERTY keyboard can consist of 80 - 110 keys. The keyboard is working like a small computer. Inside the keyboard, there is a metal plate, circuit board (key matrix) and processor, which are responsible for transferring information from the keyboard to the computer. The keyboard's processor contains the key matrix. The key matrix is a grid of circuits. These circuits are individually placed under each key. When a key is pushed, it works as an electric switch causing an electrical current to pass through the circuit, hence activating the circuit.

                                                However, depending on the working principle, there are two main types of keys. They are,

1.   Capacitive keys – Under each capacitive key, a metal plunger is fixed, which helps in activating the circuit flow. When a capacitive key is pressed, the metal plunger applies a gentle pressure to the circuit board. The pressure is identified by the computer and the circuit flow is initiated.

2. Hard contact keys - A hard contact key is attached with a metallic plate that helps in connecting the  circuit board. When the hard contact key is pressed, it pushes a metallic plate, which in turn touches  the metallic portion of the circuit plate. This overall process of completing a circuit results in a circuit  flow.  

                                                The circuit is closed when a key is pressed. Thus, the closing of the circuit signals the processor to read the keymap stored within it. The processor uses the keymap, to find the key that is closed off on the board. By using this keymap, the processor in the keyboard can tell which letter is being pushed and if it should be a capital or lowercase letter depending on if the shift key is being pressed.

                                                The keyboard connects to the computer using a PS/2 port most of the time. Both the Keyboard and the computer can send information to each other, through this connection. The processor of the keyboard sends information to the computer which key was pressed, and hence the computer can take necessary actions based on it. 

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