D Flip-Flop Simulator
Simulate an edge-triggered D flip-flop online. Set the D input, select a rising-edge or falling-edge clock, toggle the clock or generate a pulse, and observe how the stored Q and Q̅ outputs change only when the active clock edge occurs.
—
—
What Is a D Flip-Flop?
A D flip-flop is a digital storage element that stores one binary bit. It has a data input called D, a clock input, and normally two complementary outputs called Q and Q̅. The defining behavior of an edge-triggered D flip-flop is that the value present at D is copied into Q only when the configured active clock edge occurs.
At all other times, the flip-flop retains its previously stored Q value. This ability to remember a bit makes D flip-flops fundamental building blocks for registers, counters, state machines, pipelines, synchronizers and many other sequential digital circuits.
How to Use the D Flip-Flop Simulator
Choose the D input value by selecting D = 0 or D = 1. Next choose whether the flip-flop should respond to a rising clock edge or a falling clock edge. The clock can then be changed manually with the clock-level controls, toggled once, or driven through a complete pulse.
Whenever the selected active edge occurs, the simulator captures the current D value and stores it as Q. The complementary Q̅ output automatically becomes the opposite value.
Initial:
D = 1
CLK = 0
Q = 0
Rising edge:
CLK changes 0 → 1
Result:
Q captures D
Q = 1
Q̅ = 0D Flip-Flop Truth Table
For an edge-triggered D flip-flop, the important condition is whether the active clock transition occurs. On that edge, the next output state equals D. Otherwise, the previous Q state is retained.
| Clock Event | D | Q Next | Operation |
|---|---|---|---|
| Active edge | 0 | 0 | Store 0 |
| Active edge | 1 | 1 | Store 1 |
| No active edge | X | Q previous | Hold state |
D Flip-Flop Characteristic Equation
The characteristic equation of the ideal D flip-flop is very simple. At the active clock edge, the next state Q is equal to the data input D.
Q(next) = D
At active edge:
D = 0 → Q(next) = 0
D = 1 → Q(next) = 1This direct relationship is one reason D flip-flops are widely used whenever digital systems need to capture and delay a binary value by one clock event.
Rising-Edge Triggered D Flip-Flop
A positive-edge or rising-edge triggered D flip-flop captures D when the clock changes from logic 0 to logic 1. A transition in the opposite direction does not change the stored state.
Active edge:
0 → 1
D before edge:
1
Q before edge:
0
Q after rising edge:
1Falling-Edge Triggered D Flip-Flop
A negative-edge or falling-edge triggered D flip-flop performs the same storage operation, but its active transition occurs when the clock changes from logic 1 to logic 0.
Active edge:
1 → 0
D before edge:
0
Q before edge:
1
Q after falling edge:
0What Happens Between Clock Edges?
Changing D by itself does not immediately change Q in an ideal edge-triggered D flip-flop. The input can change while the flip-flop continues holding the previously stored output.
Stored:
Q = 0
Change:
D = 1
No active clock edge occurs.
Result:
Q remains 0When the next active clock edge arrives, the new D value can then be captured.
Difference Between a D Flip-Flop and D Latch
A D latch and a D flip-flop both store binary information, but they respond to their control signals differently. A D latch is level-sensitive. While its enable condition is active, changes at D can propagate to Q. An edge-triggered D flip-flop responds only to a particular clock transition.
| Feature | D Latch | D Flip-Flop |
|---|---|---|
| Control | Enable level | Clock edge |
| Sensitivity | Level-sensitive | Edge-triggered |
| Q changes | During active level | At active edge |
| Storage | 1 bit | 1 bit |
Q and Q-Bar Outputs
The normal Q output contains the stored state. The complementary output, written Q̅, /Q or Q-bar, contains the logical inverse of Q.
If:
Q = 0
Then:
Q̅ = 1
If:
Q = 1
Then:
Q̅ = 0Some physical flip-flop ICs provide both outputs, while other designs may use only Q.
Setup Time and Hold Time
A real hardware D flip-flop requires the D input to remain stable for a short period before and after the active clock edge. These intervals are called setup time and hold time. Violating those timing requirements can cause unpredictable hardware behavior or metastability.
This browser simulator models the ideal logical behavior of a D flip-flop. It does not attempt to reproduce analog timing violations, propagation delay or metastability.
Where D Flip-Flops Are Used
D flip-flops are among the most common storage elements in digital electronics. Groups of D flip-flops form registers that can store multi-bit binary words. They are also used in shift registers, synchronous counters, finite-state machines, clock-domain synchronizers and processor pipelines.
Because Q takes the D value from the active clock edge, a D flip-flop can also be viewed as a one-clock-event memory element for synchronous logic.
D Flip-Flop Timing Example
Rising-edge triggered D flip-flop
Time 0:
D=0 CLK=0 Q=0
D changes:
D=1 CLK=0 Q=0
No capture
Clock rises:
D=1 CLK=1 Q=1
Capture D
D changes:
D=0 CLK=1 Q=1
No capture
Clock falls:
D=0 CLK=0 Q=1
No capture
Clock rises again:
D=0 CLK=1 Q=0
Capture D