How it works? | Keyboard
The history of the computer keyboard has more than 150 years. The prototype of the modern keyboard are typewriters that appeared in the middle of the XIX century. First keys with the letters arranged in alphabetical order. However, over time it became clear that such an arrangement is inconvenient, because the letters are located far from the center. After 20 years it has been invented "QWERTY" keyboard -raskladka, which is still used today. How does the keyboard - this in today's issue!
Modern keyboard has buttons, a microcontroller and LED operating mode - Num Lock, Caps Lock, and others. The keys are transmitted from the computer so-called scan codes, and the BIOS or operating system in accordance with the layout of the keyboard converts scan codes in the key codes.
The buttons are read by a circuit which is called "buttons matrix" and consists of a grid of wires, which are located at the intersections of the key. When the computer is on, keyboard microprocessor sends electrical pulses in the vertical wiring in the search signal. In the normal state (when there is no pressing) lines are not closed. If the key is pressed, the vertical and horizontal wires touch, the circuit closes and the current pass through it. With this keyboard controller will understand that a keystroke occurred, and by the closed postings to determine which key was pressed. After that, it sends the scan code of the key that was actuated. Scan codes rigidly attached to each key on the hardware level, and do not depend on the state of Caps Lock, Num Lock, and others, or the state of the control indicator keys (such as the Shift and Alt). The operating system then verifies and analyzes the data on the content of the operating system commands. If such instructions are present, the computer executes them. If not, it sends the information to a running application.
At the keyboard has its own buffer - to keep the scan codes of keys pressed. Due to the buffer processor can handle a combination of several buttons are pressed simultaneously.
Modern keyboard realizes the simultaneous pressing of two keys with any combination of modifier keys like Shift. However, there are advanced keyboard, capable of recording up to six simultaneous keystrokes, and some of them and did give himself for three or four keyboards. In this case, the number of keys pressed, respectively, is increased to 18 or 24.
There are also capacitive keyboards that do not react to the circuit, and a change in capacitance and therefore triggered by incomplete pressing. In this case, current flows continuously through the circuit, and the matrix registers all of its changes caused by movement of the key-conductors closer to the circuit. This change is then compared to the symbol table, and is determined by the location of the key pressed. Speaking of the keyboard, not to mention the effect debounce. By pressing the switch-key is released while closed-opened. While ringing lasts a few hundredths of a second, it is enough that the computer has registered a few clicks.
debounce Technologies are usually embedded in the keyboard controller - after the button is pressed, it is not queried for some time, certainly longer than the duration of transients. On the first keyboard debounce time it was so great that prevent fast typing.