Electronics/Latches and Flip Flops

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Contents 1 Overview 2 Construction 3 Types 3.1 RS Flip Flops 3.2 D Flip Flops 3.3 Toggle Flip Flops 3.4 JK Flip Flops

[edit] Overview

A flip-flop (F/F) is a device made out of digital gates that uses feedback to store the previous state (1 or 0) of its input(s). Flip-flops are frequently used to latch input data, meaning that in a circuit they are fed some binary value and then hold it until the latch is turned off. All flip-flops have at least one output labeled Q. Frequently they have a complement labeled Q'. The 4 basic flip-flops are RS (or SR), D, Toggle and JK

[edit] Construction

[1]

[edit] Types

[edit] RS Flip Flops

Pin Configuration

Pin Name	I/O
R	m
S	I
Q	O
/Q	O

The simplest flip flop is the RS F/F made from either two NAND or two NOR gates. RS stands for Reset or Set this flip flops two input pins. Set and Reset are the only two modes this flip flop has. All other flip flops internal workings are built around the RS design in some way. It is the only flip flop with out a clock line of another kind.

[edit] D Flip Flops

Pin Configuration

Pin Name	I/O
D	I
CLK	I
Q	O
/Q	O

The basic D flip flop has only 2 inputs D and CLK and 1 output Q. The binary value at D has no effect on the output of the flip flop until the CLK (clock) line is triggered. To trigger the clock line it must change state. A flip flop will only trigger on either a change from high to low or low to high. This depends on its clock being active low or active high. This causes the value at that moment to be held by the flip flop at Q. The D in D flip flop stands for either Data or Delay depending on who you ask or what it is being used for. This is because the D input can ether be thought of as data being latched or some input being delayed by the triggering of the clock.

[edit] Toggle Flip Flops

Pin Configuration

Pin Name	I/O
T	I
CLK	I
Q	O
/Q	O

The basic toggle flip flop only has two inputs CLK and T. When it is toggled it's output changes. Toggle flip flops are frequently used to devide the frequency of clock signals by two.

[edit] JK Flip Flops

or

The CLK on the first symbol is equivilent to the triangle on the second symbol.

Pin Configuration

Pin Name	I/O
J	I
K	I
CLK	I
Q	O
/Q	O