A scan code is created by a computer keyboard each time a key is pressed and when it is depressed. After the keyboard has created the scan code, it is received serially by the computer on I/O port 60h. After being received, the keyboard controller informs the microprocessor that a scan code is ready to be read by issuing interrupt 9h. The computer then uses the BIOS codes to match the scan code with the corresponding key that was pressed. After the scan code is matched, the software can read the pressed keys by issuing interrupt 16h.