Abstract: An apparatus for multiplexing a pair of test clock signals and a pair of system clock signals onto a pair of output clock signals includes a first means for coupling a first test clock signal to a first output clock signal when a test mode control signal is active, for driving the first output clock signal to an inactive clock signal level when the test mode control signal transitions to an inactive state, and for coupling a first system clock signal to the first output clock signal beginning with a first full clock pulse of the first system clock signal which occurs after the test mode control signal transitions to the inactive state.