A keyboard controller in a computer accepts input from a keyboard and sends it to the CPU. It generates an interrupt signal, translates information into scan codes, and handles physical aspects of the keyboard. The controller is usually on the motherboard, but can also be emulated in other parts of the processor. The keyboard sends a signal to the controller about which keys are pressed, and the controller converts it into a scan code that is interpreted by the CPU. Modifier keys are also passed along.
A keyboard controller is a type of integrated circuit inside most computers designed to accept input from a keyboard and transmit it to the central processing unit (CPU), where it can be passed to the operating system for interpretation . In general, when a keyboard controller receives a signal from a keyboard or similar input device, it generates a signal known as an interrupt which causes the CPU to briefly halt execution so it can handle the signal that the keyboard controller is sending. Depending on different hardware specifications, a keyboard controller receives different bit sequences from the keyboard and then passes this information through a lookup table, where the information is translated into bytes known as scan codes that can be more easily interpreted by the CPU. The controller also handles the interpretation of certain physical aspects of a keyboard, such as timing key presses when a key is held down and turning on or off the light-emitting diodes (LEDs) that indicate lockout numbers or caps lock on the keyboard itself.
The location of the keyboard controller can vary, but the integrated circuit is traditionally on the computer motherboard. In cases where the keyboard is not an integral part of the computer, the controller is almost never inside the keyboard hardware. The opposite is true for keyboards that are part of the computer structure, such as in a laptop. There are also situations where there is no separate keyboard controller but the functionality is emulated across other parts of the processor.
Hardware found inside a traditional computer keyboard sends information to the controller about which keys have been pressed, usually by measuring a change in the current under individual keys. This signal is standardized by a circuit similar to the keyboard controller in the computer. This means that each keyboard knows its topography, the location and layout of the keys and can send the same signal when a user presses the Enter key, regardless of where the key is located on the keyboard or the physical design of the keyboard. .
The controller inside the main computer takes this signal and converts it into a scan code, which is more easily interpreted by the CPU. Modifier keys, such as Shift or Ctrl, are passed along with all other key presses. At this point, the keyboard controller sends a signal to the CPU causing it to stop its current action and retrieve the scan codes. The CPU then passes the scan codes to the system where, in many operating systems, a system event is generated and broadcast for processing by the active program.
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