Non-volatile memory devices for outputting data using double data rate (DDR) operations and methods of operating the same

A non-volatile memory device is operated by outputting data in response to an alternating sequence of first and second edges of a read control signal, respectively. A determination is made whether the read control signal and a write control signal are in synchronization at one of the first edges. Output of the data is stopped at the second edge that follows the one of the first edges of the read control signal if the read control signal and the write control signal are in synchronization at the one of the first edges.