An integrated circuit and a code generating method are described. The integrated circuit includes a plurality of field effect transistors, a plurality of sense-amplifiers, and a processing circuit. Each field effect transistor is configured to represent an address in a mapping table and includes a source, a drain, a channel and a gate. Each sense-amplifier is connected to the drain and configured to sense an electric current from the drain and identify a threshold voltage of the corresponding field effect transistor. The processing circuit is configured to categorize each of the threshold voltages identified by the corresponding sense-amplifiers into a first state and a second state and mark the state of each of the threshold voltages at the corresponding address in the mapping table.