Edge Trigger

A digital signal has two discrete levels: a high level and a low level. When the signal transitions from high to low or from low to high, a digital edge is created. There are two types of edges: rising, which occurs when the signal transitions from low level to high level, and falling, which occurs with a transition from high level to low level. Triggers configured to act on a rising or falling edge of a digital signal are called edge triggers.

As the following figure shows, an edge trigger could be configured to occur either at the place labeled Falling Edge of Signal or at Rising Edge of Signal.