course 1: Input Units

Input Units The most common input device is the keyboard. It is standard equipment on virtually every personal computer, keyboard is an device used to convert the keystrokes in to the electrical signals that a computer can understand. There are special types of switches and circuits to do this. Keyboard contains its own internal processor that takes electrical signals through key strokes.

The microprocessor and controller circuitry of a keyboard.
The basic elements of a keyboard are a switch matrix (key matrix) and a keyboard interface encoder chip. The switch matrix consists of a number of horizontal and vertical lines crossing each other, at each crossing, a small switch operated by a spring –loaded key is located. The keyboard encoder is a microprocessor with an in-built ROM.

A look at the switch matrix
The key matrix is the grid of circuits underneath the keys. Pressing the key bridges the gap in the circuit, allowing a tiny amount of current (التيار) to flow through. The processor monitors the key matrix for signs of continuity at any point on the grid. When it finds a circuit that is closed, it compares the location of that circuit on the key matrix to the character map. The character map is basically a comparison chart جدول مقارنة for the processor that tells it what the key at x, y coordinates in the key matrix represents. If more than one key is pressed at the same time, the processor checks to see if that combination of keys has a designation in the character map. For example, pressing the a key by itself would result in a small letter "a" being sent to the computer. If you press and hold down the Shift key while pressing the a key, the processor compares that combination with the character map and produces a capital letter "A."
Each key on the board has a little electrical switch (capacitor) under it. When you press a key, its switch completes a certain electrical circuit and a processor (inside the keyboard) records which circuits were completed and in what order.