A timing controller includes a count control circuit, a pulse width detector, and a pulse generator. The count control circuit receives an external enable signal. Pulses of the external enable signal include an effective and a blank period of image data. The count control circuit counts pulse widths of each of the pulses. The pulse width detector receives the counted pulse widths, compares a pulse width of a present pulse with pulse widths of previous pulses, and detects a pulse width of a previous pulse that has a pulse width smaller than the pulse width of the present pulse. The pulse generator generates three output pulses having pulse widths that are one-third a period of the detected previous pulse. The pulse generator outputs the first, second and third pulses as an internal enable signal.