Wednesday, 24 July 2019

All about flip Flops

What is a flipflop ?

This is not about the things you wear on your feet.

Rather, Flip flops are a form of data storage.
They are also called Latches or bistable multivibrators.
They are digital circuits.made up of bits : 0 or 1

Flip flops can store one of two states
0 = logical low
1 = logical high

Using these 1s and zeros, we can express any data of any size.
Digital circuits make use of these binary digits.

So to emphasise, a flip flop is a way to store digital data.
They are effectively 1-bit memory cells allowing circuits to store data and deliver it at a later time. One result of this is that they can turn an impulse into a constant signal, "turning a button into a lever".

In the synthesizer world, flip flops can be found in many devices (like sequencers).
Digital hardware that requires data storage (like pitch or trigger information) will likely use flip flops.
By connecting multiple flip-flops in the right way you can make shift registers, storage registers, and counters. 

The simplest flip flop will store a bit at it's output.
ie either a zero or a one (at its output).
When we change the input (to the flip flop) the output will of course also change.
Unlike simple logic gates, flip-flops use feedback. This is important in creating sequential logic circuits as opposed to combinational logic circuits.

There are several basic types of Flip flops. Their input lines are labeled according to their purpose (Set, Reset, Toggle, Data, Clock). The output is commonly labeled Q & "inverse output" Q̅.
Q̅ is always ON when Q is OFF and vice versa.

Flip flops can be designed to respond to the level of a signal or be triggered by a change in the signal.
Level = Latch
Change = flip- flop

Types of Flip-flops:

1) SR- Flip flops.
      a) Using NAND gates
      b) Using NOR gates

2) D-flip flops

3) JK-flip flops

4) T-flip flops

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1) SR - Flip flops

(SR = Set Reset)

The SR flipflop comes in two varieties: NAND & NOR.
These refer to the gates that make up the flip flop.
The SR flip flop is also "non-clocked".

The diagram is very simplified:.

You may see a flip drawn like this:
  You have two boxes made up of NAND and NOR gates

Each flipflop  has 2 outputs.  "Q" and "not Q"
Each flipflop has two inputs : S & R

The outputs are connected to opposing gate inputs.

This is what a NAND gate flip flop looks like

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2) D- Type flip flop.


D stands for Delay or Data
This is an example of a clocked flip flop
It's symbol is:
There are 2 inputs : Clock & Data.
There are 2 outputs: Q & not Q.

It only transfers data at a certain time of the clock cycle.
When the clock goes high ( 0 or 1) data will be transferred to Q.
When the clock goes low, Q remains unchanged..
 It can be viewed as a delay line.


The D input condition is only copied to the output Q when the clock input is active.
When the clock goes low, the flip flop wont change its state (until another clock high is reached).
It will store whatever data was present on its output before the clock transition occurred.


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3) JK-flip flops


This is basically a gated SR flip flop, but a clock input is added.
There are 2 inputs labelled J & K, plus a clock input.
This is the circuit symbol for a +ve edge triggered JK flip flop.
J = set (Jump)
K = reset (Kill)

The flip flop responds differently depending on the values of J & K
When the clock is triggered, the latch's output can be set, reset, toggled, or left as is, depending on the combination of J and K.
J = K = 1 condition to Toggle or flip
J = 1, K = 0 is a command to set the flip-flop
J = 0, K = 1 is a command to reset the flip-flop


The JK flip flop is very flexible as you can make it behave like other flip flops (SR, T & D).
For example,
To make a D flip-flop, simply set K equal to the complement of J.
To make a T flip-flop, set K equal to J.

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4) T flip Flop


T = Toggle. (think of a toggle light switch)
This type of flip flop changes its output on each clock edge.
The type of clock edge is important. .... negative or positive?

Whenever the toggle is triggered, the latch changes its state from OFF to ON or vice versa.


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Examples of Flip-flops

74LS73 - Dual JK-type Flip Flops with Clear (LS TTL)
74LS76 - Dual JK-type Flip Flops with Preset and Clear (LS TTL)
74LS107 - Dual JK-type Flip Flops with Clear (LS TTL)
74LS109 - Dual Pos-Edge-Trig J-K Flip-Flop (LS TTL) 
74LS273 - CMOS Latch (Ken Stone's CGS11 - D/A converter)
74HC112 - Dual Neg-Edge-Trig J-K Flip-Flop (CMOS)
74HC393 - flop flop (Hyve Synth
4027B - Dual JK-type Flip Flop (CMOS)

74LS74 - Dual D-type Flip Flops with Preset and Clear (LS TTL)
74100 - Dual 4-bit Latch (Texas Instruments) 
74174 - Flip Flop  LZX Flip Flop Hex w/ Clear  (74HC174)
74LS175 - Quad D-type Flip Flops with Clear (LS TTL)
74LS273 - Octal D-type Flip Flops with Clear (LS TTL)
4013B - Dual type D Flip Flop (Standard CMOS) -- NLC flip flop chaos, NLC Divide & C
40174B - Hex D-type Flip Flop with Master Reset (Standard CMOS)
4042 -  Quad D-Latch (CMOS)
4514 - Four Bit Latch / 4-16 Line Decoder


Links
+ TTL - transistor-transistor logic  
+ DIY Index
+ CMOS
+ How did NASA steer the saturn V - the computer & data storage in the 1960s (memory module)
+ LVDC - The saturn V memory module


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