A DFF records (or registers) new data whenever an active clock edge occurs-the active edge can be either the rising edge or the falling edge. A clock signal is most typically a square wave that regularly repeats at some frequency. The timing control input, called “clock”, is used to coordinate when new data can be written into the memory element, and conversely, when data cannot be written. The 'D' in DFF arises from the name of the data input thus, the flip-flop may also be called a data flip-flop. A DFF typically has three inputs: a data input that defines the next state, a timing control input that tells the flip-flop exactly when to “memorize” the data input, and a reset input that can cause the memory to be reset to '0', regardless of the other two inputs. A D flip-flop modifies the function of a D-latch in a fundamental and important way: the next state (or D input) can only be written into the memory on the edge (or transition) of the timing signal.Ī D flip-flop (DFF) is one of the most fundamental memory devices. In a D-latch, the present state and next state are the same as long as the timing control input is asserted.
1, the current output of a memory device is called the “present state”, and the input is called the “next state” because it will define the memory at the next assertion of the timing control input. USB Scopes, Analyzers and Signal GeneratorsĪll useful memory devices have at least two inputs-one for the data signal to be memorized, and a timing control signal to define exactly when the data signal should be memorized.