Flip Flop Basics

Flips Flops...when I first encountered them in ENEE244 I had no idea what they were besides a funny name. I came into the course knowing absolutely nothing about digital components or really how a computer functioned on the hardware level.

What I am going to briefly cover here (in probably a multiple part series due to the important nature of the material) is the essence of chapter 6 in Givones book.

Basic logic elements and, or, not xor, etc gates have well defined uses and are easy to see how to implement. If your basic circuit or task requires you to two input sources to be logical 1, or high (1 in the binary world, or typically +5 volts) in order for the output to be a logical 1 you would use an and gate.

Flip-Flops are a sequential network, or one that has "memory" and are its heart is a bistable element.

This is the first hurdle one must conquer, understanding how this works. Imagine X is a 0, then the output of the top not gate will be logical 1. this is also connected to the input of the lower not gate and therefore its output or Q' is logical 0. It is a complementary device and one might wonder well it seems common sense, but what are its applications?

Good Question! This is were Flip-flops come in to play, they are bistable elements that also have inputs and will hold their output states as long as it is connected to some power source (usually denoted Vcc). We will consider synchronous flip flops that run off of a clock in order to function.

We will skip over latches as they are essentially identical to flip-flops except for the fact that they respond continuously to inputs...they are level triggered.

You can have many different types, SR, D, T, and JK. They all have their own specific truth table but have the same underlying function of storing a piece of information.

What you can do with these is the interesting part. Any system you want to build or design can be constructed using flip-flops if it needs some form of memory.  A Shift Register is a great example of a simple flip-flop implementation and will be covered in the next article! More complex examples include computer memory.

Flip-flops take some time to really understand and my goal is to have some "sample projects" as the focus of the next couple articles to walk through the actual design process.