These devices are positive edge triggered flip-flops. The difference between HD74HC564 and HD74HC574 is only that the former has inverting outputs and the latter has noninvertering outputs. Data at the D inputs, meeting the set-up and hold time requirements, are transferred to the Q or Q outputs on positive going transitions of the clock (CK) input. when a high logic level is applied to the output cotrol (OC) input, all outputs go to a high impedance state, regardless of what signals are present at the other inputs and the state of the storage elements.