A digital device is provided. The digital device uses three states, including a ground (GND) state, a voltage (VDD) state, and a FLOAT state. On designing a chip, two storage units and a pad circuit are set inside; the pad circuit comprises a current limiter and two switches; and less ports contained are required than the conventional. That is, one port obtains three states. As comparing to the conventional having only two states, the present invention uses the port connected with two storage units in the pad circuit for obtaining the three states; a circuit featuring “pull up” and “pull down” is used to identify the state of connection of the port; and the port determines a plurality of definitions through the three states of GND, VDD and FLOAT. Thus, a pad is saved for reducing the space and cost of the chip.