Abstract: A scan method for keyboards is firstly to set a higher voltage or a lower voltage to a keyboard scan input/output port when a low voltage signal is generated at a keyboard scan input port, and then to detect a voltage at the keyboard scan input/output port or the keyboard scan input port so as to determine whether the detected low voltage signal is a valid button-depressed signal or a noise. Further, a grounding resistor is connected electrically to the keyboard scan input/output port, and the scan method prevails as well to determine whether or not a detected low voltage signal is a valid button-depressed signal.