What is a Flip Flop? The first thing that comes to mind to any person's mind is the sandal. Well... in the world of Digital Electronics a Flip Flop has almost nothing in common with the sandal that everyone is familiar with. The exact definition of a flip flop is; A digital logic circuit that can be in one of two states which it switches (or "toggles") between under control of its inputs.
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Types of Flip Flops There are a few different types of flip flops, but the main ones used are the D flip flops and the JK flip flops, and no, that doesn't stand for Just kidding. :)
The D flip flop is a little less complex then the JK flip flop, it is the more basic type. Below the very first picture is a D Flip Flop. Then next is a JK. |
D Flip Flop (AKA... 74LS74N)
In a D Flip flop, D; is the input. It can be whatever it wants to be, or whatever the logic leading up to it tells it to be. Q (the output) looks at D to see what it is, and Q' (Q not, the one with the line above it) also looks at D, but it is the opposite of it. So if D is a logic 1, Q' is then a logic 0. The clock Input is where the clock goes. A clock is required to create a pulse, on each pulse Q will check with D and preset and clear will also be checked. Speaking of present and clear, they take precedence over anything else going on in the flip flop. They can reset it or clear everything anytime.
Clock Pulse: Q, D, and Q' Relationship
To the right is a picture of the pulsating clock, because this is an up counter, each time the clock pulses on an up count Que checks with Dee, Present, and Clear, to determine what its going to be, high is 1 and low is 0.
When D is 1, Q=1, Q'=0 (on each up rising edge)
When D is 0, Q=0, Q'=1 (On each rising edge)
When D is 1, Q=1, Q'=0 (on each up rising edge)
When D is 0, Q=0, Q'=1 (On each rising edge)
JK Flip Flop (AKA... 74LS76N)
A Jk Flip flop is similar to a D Flip Flop, the only difference is Q doesn't "look" at D to determine what it's output will be. Instead it looks at J and K. Below is a table that shows what will happen to Q when J and K are either 1 or 0. In a JK flip flop, the Clock, Preset, Q not, and Clear, all still play the same role as they did in the D Flip flop.
To the left is the table of possible J and K values and the corresponding Q output. To the right is a diagram of a JK flip flop.
To the left is the table of possible J and K values and the corresponding Q output. To the right is a diagram of a JK flip flop.