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Flip Flops Overview
A flip flop is known as a sequential logic element. It is, not surprisingly, a fundamental building block for creating sequential logic circuits. Some examples of this type of circuit include shift registers and counters. These types of circuit depend not only on a set of inputs, but also their past inputs to work correctly.
For example, let us say you want to design a circuit that will count from zero to three, in steps of one, every time a switch is pressed. A simple switch can only have two possible states. It can either be switched on, or switched off. Yet each time the switch is pressed, we want the circuit to display a different output state. For example:
- Press switch once. The output changes from 0 to 1.
- Press switch again. The output changes from 1 to 2.
- Press switch again. The output changes from 2 to 3.
From this example it can be seen that the circuit will only work correctly if it somehow 'remembers' its previous state. Flip flops have the ability to remember their past history and are often referred to as bistable devices (a device with two stable states).