Abstract: A scan chain circuit is disclosed. The scan chain circuit includes a chain of serially coupled clocked circuits. In a first mode of operation, each of the clocked circuits toggles in response to a rising edge of a clock signal. In a second mode of operation, a first set of the clocked circuits in the chain of serially coupled clocked circuits toggle in response to the rising edge of the clock signal and a second set of the clocked circuits in the chain of serially coupled clocked circuits toggle in response to a falling edge of the clock signal.