A D flip-flop (Data or Delay flip-flop) is a simple and commonly used digital memory element that stores a single bit of data. It's widely used in digital circuits, especially for data storage, registers, and counters.

Structure:

The D flip-flop has two inputs:

• D (Data): The value to be stored.
• Clock (CLK): Controls when the flip-flop stores the input value.

It has two outputs:

• Q: The current stored value.
• Q̅ (Q-bar): The inverse of the stored value (complement of Q).

Key Points:

1. Edge-Triggered: The D flip-flop is usually edge-triggered, meaning it stores the input value only when there’s a rising or falling edge of the clock signal. The most common type is positive edge-triggered, where the data is captured at the moment the clock signal goes from 0 to 1 (rising edge).

2. Working:

   • When Clock is High (Rising Edge): The value at the D input is transferred to the output Q.
   • When Clock is Low (No Edge): The output Q remains unchanged, and the flip-flop "holds" its value.

   This makes the D flip-flop behave like a latch, where the output follows the input at specific times, determined by the clock.