CENT-113 Digital Electronics 1 Flip Flops TI Type 502 Flip Flop: 1st production IC in 1960.

CENT-113 Digital Electronics1

Flip Flops• TI Type 502 Flip Flop: 1st production IC in 1960.


Interest• 1919: W. H. Eccles and F. W. Jordan publish the first

flip-flop circuit design.• M74HC74AM Fairchild CMOS flip-flop for frequency

manipulation is used in a Smart Card Reader.


Logic Circuit Classifications• Combination Logic Circuits

– Building block is the logic gate.– Use AND, OR, NOT gates.

• Sequential Logic Circuits– Building block is the flip flop (FF).– Used in timing and memory devices.– Flip Flops are wired to form counters, shift registers,

and various memory devices.


R-S Flip Flop• Logic Symbol Wiring Diagram

Set

Reset Complementary

NormalS

R

Q

Q

FF

• Truth Table Waveform DiagramMode of

OperationInput

SInput

ROutput

QOutput

QEffect

Prohibited 0 0 1 1 ProhibitedDo not use

Set 0 1 1 0 For settingQ to 1

Reset 1 0 0 1 ResettingQ to 0

Hold 1 1 Q Q DependsPrevious

State

Input Output

Input

Output

Set Reset SetHold

S

R

Q

Q

Hold10

10

10

10

Also called:R-S Latch

Set-Reset FF


Clocked R-S Flip Flop• Logic Symbol Wiring Diagram

• Truth Table Waveform DiagramMode ofOperati

on

InputCLK

InputS

InputR

OutputQ

OutputQ

Effect

Hold 0 0 1 1 NoChange

Reset 0 1 0 1 Reset or cleared

to 0

Set 1 0 1 0 Set to 1

Prohibited1 1 1 1 Do not

use

Input

Output

S

R

Q

Q

10

10

10

10

Set

Reset Complementary

NormalInput Output

ClockS

R

Q

Q

FF

CLK

CLK

Output FF operates Synchronously

in step with clock.


Questions• Q. What type of waveform is used in flip flops?

• A. Square Waves.

• Q. What does the RS stand for in the RS Flip Flop?

• A. Reset Set.


D Flip Flop• Logic Symbol Wiring Diagram

Data

Clock Complementary

NormalD

CLK

Q

Q

FF

• Truth Table Similar Wiring

Input Output

Also called:Delay FFData FF

D-type Latches‘Delayed 1

Clock Pulse’

Input

CLKInput

DOutput

Qn+1

Output

Q

0 0 1

1 1 0

D

CLK

Q

Q

FF

S

R

Q

Q

FF

CLK =


7474 D Flip Flop• Logic Symbol

• Truth Table

Data

Clock Complementary

NormalD

CLK

Q

Q

FFInput Output

Mode ofOperation

INPUTS OUTPUTSAsynchronous Synchronous

PS CLR CLK D Q Q

Asynchronous Set 0 1 X X 1 0

Asynchronous Reset 1 0 X X 0 1

Prohibited 0 0 X X 1 1

Set 1 1 L to H 1 1 0

Reset 1 1 L to H 0 0 1

Note: The asynchronous inputs(PS & CLR) Override the synchronous inputs (D & CLK) .

PS

Preset

ClearCLR


D (Delay) Flip Flop Uses• Sequential logic devices used in temporary

memory devices.

• Wired together to form shift registers and storage registers.

• Delays data from reaching output Q one clock pulse.

• CMOS examples: 74HC74, 74FCT374, 40174

• Over 50 different ICs in FACT CMOS family.


J-K Flip Flop• Logic Symbol

• Truth Table Mode of

OperationINPUTS OUTPUTS Effect

InputCLK

InputJ

InputK

OutputQ

OutputQ

Hold 0 0 NoChange

NoChange

NoChange

Reset 0 1 0 1 Reset or cleared to 0

Set 1 0 1 0 Set to 1

Toggle 1 1 Toggle Toggle Changed toOpposite State

Data

Complementary

NormalInput Output

ClockJ

K

Q

Q

FF

CLK

Data


7476 J-K Flip Flop• Logic Symbol

• Truth Table Mode ofOperation

INPUTS OUTPUTSAsynchronous Synchronous

PS CLR CLK J K Q Q

Asynchronous Set 0 1 X X X 1 0

Asynchronous Reset 1 0 X X X 0 1

Prohibited 0 0 X X X 1 1

Hold 1 1 0 0 No Change No Change

Reset 1 1 0 1 0 1

Set 1 1 1 0 1 0

Toggle 1 1 1 1 Opposite State

Note: 7476 uses the entire pulse totransfer data from J & K data inputsto Q & Q outputs.

Data

Complementary

NormalInput Output

ClockJ

K

Q

Q

FF

CLK

Data

Preset

ClearCLR


J-K Flip Flop Uses• Universal Flip Flop. Has all features of other FF.

• When being used only in the toggle mode, commonly called a T Flip Flop.

• CMOS examples: 74HC76, 74AC109, 4027.

• Most commonly used as counters.


Questions• Q. What circuit can be used to give a clock

signal?

• A. Astable multivibrater.


IC LatchesInput

Keyboard

7 8 9

1

4 5 6

2 3

0

Encoder 4-Bit Latch Decoder

OutputDisplay

Decimal DecimalBinary

•A device that serves as a temporary buffer memory is called a latch. An example of a 4-bit latch is the 7475.•A latch is transparent when the enable input is high, the normal outputs follow the data in the D inputs.•One example of flip flops is to latch or hold data.


IC Latch Uses• The latch is the fundamental memory device

used in digital electronics.

• Almost all digital equipment contains simple memory devices called latches.

• CMOS examples: 4042, 4099, 74HC75

• 4043 is an example of a BCD-7 Segment latch/decoder/driver chip.


CMOS D Flip-Flop Schematic


D Flip Flop using Nor gatesWhat logic gates are more efficient?


CMOS D Flip-Flop • CMOS technology allows a very different

approach to flip-flop design and construction. Instead of using logic gates to connect the clock signal to the master and slave sections of the flip-flop, a CMOS flip-flop uses transmission gates to control the data connections.


Triggering Flip Flops• The added inverter bubble at the clock input

shows that triggering occurs on the negative going edge of the clock pulse.

• The J-K master/slave flip flop uses the entire pulse (positive edge and the negative edge) to trigger the flip flop.

• Waveform 165.


Schmidt Trigger• Schmidt Trigger Inverter commonly used to

square up input signal. This reshaping of the waveform is called signal conditioning.


IEEE vs. Logical Symbols• See internet links.


Conclusions• Q. What are some circuit uses for flip flops?

• A. Counters, shift registers, and various memory devices.

CENT-113 Digital Electronics 1 Flip Flops TI Type 502 Flip Flop: 1st production IC in 1960.

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