In electronics, a signal edge is a transition of a digital signal from low to high or from high to low:
A rising edge (or positive edge) is the low-to-high transition. A falling edge (or negative edge) is the high-to-low transition. In the case of a pulse, which consists of two edges:
The leading edge (or front edge) is the first edge of the pulse. The trailing edge (or back edge) is the second edge of the pulse.
See also Flip-flop (electronics), an edge-triggered circuit Rise time, for a signal transition
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