![]() Whenever we enable a multivibrator circuit on the transitional edge of a square-wave enable signal, we call it a flip-flop instead of a latch. There is such a thing as negative edge triggering as well, and it produces the following response to the same input signals: This is known as positive edge-triggering. In the second timing diagram, we note a distinctly different response in the circuit output(s): it only responds to the D input during that brief moment of time when the enable signal changes, or transitions, from low to high. ![]() When the enable signal falls back to a low state, the circuit remains latched. In the first timing diagram, the outputs respond to input D whenever the enable (E) input is high, for however long it remains high. Let’s compare timing diagrams for a normal D latch versus one that is edge-triggered: D Latch Timing Diagram One method of enabling a multivibrator circuit is called edge triggering, where the circuit’s data inputs have control only during the time that the enable input is transitioning from one state to another. In many digital applications, however, it is desirable to limit the responsiveness of a latch circuit to a very short period of time instead of the entire duration that the enabling input is activated. The latch responds to the data inputs (S-R or D) only when the enable input is activated. So far, we’ve studied both S-R and D latch circuits with enable inputs.
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