These devices contain two independent D-type positive-edge-triggered flip-flops.
A low level at the preset or clear inputs sets or resets the outputs regardless of the levels of the other inputs . When preset and clear are inactive(high), data at the D input meeting the setup time requirements are transferred to the outputs on the positive-going edge of the clock pulse. Clock triggering occurs at a voltage level and is not directly related to the rise time of the clock pulse. Following the hold time interval, data at the D input may be charged without affecting the levels at the outputs.