Better to know some
... than all
"Flip-flop" is the common name given to two-state devices which offer basic memory for sequential logic operations. Flip-flops are heavily used for digital data storage and transfer and are commonly used in banks called "registers" for the storage of binary numerical data.
Edge triggering is when the flip-flop state is changed as the rising or falling edge of a clock signal passes through a threshold voltage. This true dynamic clock input is insensitive to the slope or time spent in the high or low state.
Figure: A slow or delayed gate can be used to convert a level change into a short pulse. Both types of dynamic triggering are represented on a schematic diagram by a special symbol near the clock input. In addition to the clock and data inputs most IC flip-flop packages will also include set and reset (or mark and erase) inputs. The additional inputs allow the flip-flop to be preset to an initial state without using the clocked logic inputs.
Figure: The schematic symbols for
a) a positive edge-triggered JKFF,
b) a negative (falling) edge-triggered JKFF and
c) a negative edge-triggered JKFF with set and reset inputs.