An input/output device comprises a bonding pad, a signal transport circuit, and a blocking unit. The signal transport circuit has a first terminal connected to the bonding pad and a second terminal connected to a core circuit of an IC product. The signal transport circuit is capable of transporting a signal either from the bonding pad to the core circuit or from the core circuit to the bonding pad. The blocking unit has a control terminal and is coupled between the bonding pad and the signal transport circuit. The control terminal is coupled to receive an enable signal. The blocking unit ties the bonding pad to a predetermined voltage level when the enable signal is de-asserted, thereby blocking the signal transport provided by the signal transport circuit. The blocking unit unties the bonding pad from the predetermined voltage level when the enable signal is asserted.