Page "Digital" Paragraph 5

Devices with many switches ( such as a computer keyboard ) usually arrange these switches in a scan matrix, with the individual switches on the intersections of x and y lines.

When a switch is pressed, it connects the corresponding x and y lines together.

Polling ( often called scanning in this case ) is done by activating each x line in sequence and detecting which y lines then have a signal, thus which keys are pressed.

When the keyboard processor detects that a key has changed state, it sends a signal to the CPU indicating the scan code of the key and its new state.

The symbol is then encoded, or converted into a number, based on the status of modifier keys and the desired character encoding.