Applications of Flip-Flops

Applications of Flip-Flops

AU: Dec.-07.08, May-11

Some of the important applications of flip-flops are :

• It can be used as a memory element.

• It can be used to eliminate key debounce.

• It is used as a basic building block in sequential circuits such as counters and registers.

• It can be used as a delay element.

Bounce Elimination Switch

• For interfacing keys to the digital systems, usually push button keys are used.

• Push button keys when pressed bounces a few times, closing and opening contacts the before providing a steady reading, as shown in the Fig. 2.7.1.

• Reading taken during bouncing period may be faulty. This problem is known as key debounce.

• The problem of key debounce is undesirable and it must be avoided.

• One way to avoid key debounce problem is to use SR latch.

• The circuit used to avoid keybounce with SR latch is called a switch or contact debouncer.

• The Fig. 2.7.2 shows the switch debouncer circuit and its waveforms.

• When key is at position A, the output of SR latch is logic 1 and when key is at position B, the output of SR latch is logic 0.

• When key is in between A and B, SR inputs are 00 and hence output does not change, preventing debouncing of key output.

• We can say that the output does not change during transition period, eliminating key debounce.

Review Questions

1. Explain the need for key debounce circuit.  AU Dec.-07, Marks 8

2. What are the advantages of debounce circuit ?  AU: Dec.-08, Marks 2

3. Explain the working principle of switch debounce logic.  AU May-11, Marks 6