An IC includes first and second pads. The first pad is configured to receive an external clock. Alternatively, the first and second pads are configured to be coupled to a crystal oscillator and receive a reference clock. Alternatively, the second pad is configured to be grounded. The IC includes an internal oscillator for generating an internal clock, and an oscillator detector coupled to the second pad. The oscillator detector includes a transistor having a gate coupled to the second pad configured to pull a source-drain region to a first state if the second pad receives the reference clock or allow the source-drain region to be pulled to a second state if the second pad is grounded. The IC includes a buffer for transferring the first state to the internal oscillator for keeping the internal oscillator enabled and transferring the second state to the internal oscillator for disabling the internal oscillator.