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Ee2 chapter12 flip_flop

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  • 1. IT2001PAEngineering Essentials (2/2)Chapter 12 - Flip Flop Lecturer Namelecturer_email@ite.edu.sg Nov 20, 2012Contact Number
  • 2. Chapter 12 - Flip FlopLesson ObjectivesUpon completion of this topic, you should be able to: Determine the operations of various types of flip-flops in digital circuits (e.g. JK flip-flop). IT2001PA Engineering Essentials (2/2) 2
  • 3. Chapter 12 - Flip FlopSpecific Objectives Students should be able to :  Draw the symbol of a JK flip-flop.  Explain the characteristics of a JK flip flop with the aid of a truth table.  Differentiate between edge and level triggered flip flops.  Draw the symbols of :  D type flip flop  JK flip flop and  T flip flop IT2001PA Engineering Essentials (2/2)
  • 4. Chapter 12 - Flip FlopSpecific Objectives Students should be able to :  Describe with the aid of truth tables the operation of the following flip flops :  D type flip flop  JK flip flop  T flip flop  Draw the output waveforms of the following flip flops, for a given clock and control input waveforms:  D type flip flop  JK flip flop  T flip flop IT2001PA Engineering Essentials (2/2)
  • 5. Chapter 12 - Flip FlopSpecific Objectives Students should be able to :  Explain the following terms :  Prohibited state  Indeterminate state  Synchronous and  Asynchronous IT2001PA Engineering Essentials (2/2)
  • 6. Chapter 12 - Flip FlopIntroduction  Flip-flop is digital circuit which functions as a memory element used in the digital system.  Flip-Flop is made up of an assembly of logic gates. Even though a logic gate, by itself, has no storage capability.  Flip-Flop is also known as latch and bi-stable multi- vibrator. IT2001PA Engineering Essentials (2/2) 6
  • 7. Chapter 12 - Flip FlopGeneral Flip-flop Symbol The symbol shows two outputs, labeled Q and Q, that are the inverse of each other Q FF outputs The FF can has one or inputs more inputs. These inputs Q are used to cause the FF to switch back and forth between its possible output states IT2001PA Engineering Essentials (2/2) 7
  • 8. Chapter 12 - Flip FlopGeneral Flip-flop Symbol Flip-Flop has two allowed output states. SET state :- Q where Q = 1and Q = 0. FF outputs inputs Q RESET state :- where Q = 0 and Q = 1. Thus, flip-flop is also known as bi-stable multi-vibrator or latch. IT2001PA Engineering Essentials (2/2) 8
  • 9. Chapter 12 - Flip FlopVarious Types of Flip-Flops Unclocked RS flip-flop or latch Clocked RS flip-flop or gated RS flip-flop JK flip-flop D-type latch D-flip-flop T-flip-flop IT2001PA Engineering Essentials (2/2) 9
  • 10. Chapter 12 - Flip Flop Advantage of JK Flip-Flop Does not have the problem of a  prohibited input combinations May be edge-triggered or level-triggered IT2001PA Engineering Essentials (2/2) 10
  • 11. Chapter 12 - Flip FlopPositive edge-triggered Symbol J Q CLK K Q FF triggers on positive transition IT2001PA Engineering Essentials (2/2) 11
  • 12. Chapter 12 - Flip FlopNegative edge-triggered Symbol J Q CLK FF triggers K Q on negative transition IT2001PA Engineering Essentials (2/2) 12
  • 13. Chapter 12 - Flip FlopPositive edge-triggered Logic circuit J S Q Q CLK K R Q Q IT2001PA Engineering Essentials (2/2) 13
  • 14. Chapter 12 - Flip FlopPositive edge-triggered Truth Table J K CLK Q Remark 0 0 Q O No change 1 0 1 Q = J when J = K 0 1 0 Q = J when J = K 1 1 Q O Toggle state IT2001PA Engineering Essentials (2/2) 14
  • 15. Chapter 12 - Flip FlopPositive edge-triggered Timing diagram 1 J 0 1K 0 1CLK 0 a b c d e f g h i j k 1 Q 0 IT2001PA Engineering Essentials (2/2) 15
  • 16. Chapter 12 - Flip FlopNegative edge-triggered Operates in the same manner as the positive edge- triggered except that output changes states only on the negative edge of the clock signal. IT2001PA Engineering Essentials (2/2) 16
  • 17. Chapter 12 - Flip FlopNegative edge-triggered Timing diagram 1 J 0 1K 0 1CLK 0 a b c d e f g h i j k 1 Q 0 IT2001PA Engineering Essentials (2/2) 17
  • 18. Chapter 12 - Flip FlopD Flip-Flops The D flip-flop is also D S Q called Delay or Data flip- flop. R Q The D flip-flop has only one input. It can be easily D J Q implemented from the RS or JK inputs as shown. K Q IT2001PA Engineering Essentials (2/2) 18
  • 19. Chapter 12 - Flip FlopD Flip-Flops Edge-triggered D FF Truth table D Clk Q D Q X 0 no change CLK Q 0 0 1 1 Q follows D on the“don’t care”of the clock pulse. “ X ” indicates rising edge IT2001PA Engineering Essentials (2/2) 19
  • 20. Chapter 12 - Flip FlopD Flip-Flops D =1, ClkD Clk == 1, =Q == Q = 0and 0 = 1 D = 0,= = 0, Clk Clk 1 and Q = Q D and and Initaily Q = 1 D Q D Clk CLK Q Q Waveform diagram for a D flip-flop IT2001PA Engineering Essentials (2/2) 20
  • 21. Chapter 12 - Flip FlopD Flip-Flops Level-triggered D FF Truth table D EN Q D Q X 0 no change EN Q 0 1 0 1 1 1 Q follows D when the FF is enabled; i.e. when EN = 1 IT2001PA Engineering Essentials (2/2) 21
  • 22. Chapter 12 - Flip FlopD Flip-Flops D =1,=1, EN0 andand= 0EN EN1 andand=Q = 1 D D =0, EN = D =D == 1 = = 0 Q 1 EN = = 1 1 and Q = 0 Q 1, 0, Q “Latched” “Transparent” Both D and EN inputs are 0, and Q = 0 D Q D EN EN Q Q Waveform diagram for a D flip-flop IT2001PA Engineering Essentials (2/2) 22
  • 23. Chapter 12 - Flip FlopImplementation of the D FF From the clocked RS FF by • connecting an INVERTER to the inputsD S Q D QCLK CLK CLK R Q Q IT2001PA Engineering Essentials (2/2) 23
  • 24. Chapter 12 - Flip FlopImplementation of the D FF From the clocked JK FF by • connecting an INVERTER to the inputsD J Q D QCLK CLK CLK K Q Q IT2001PA Engineering Essentials (2/2) 24
  • 25. Chapter 12 - Flip FlopAsynchronous Inputs S R Q Q Remark 0 0 1 1 Prohibited state 0 1 1 0 Set state, Q =1 1 0 0 1 Reset state, Q = 0 1 1 0 1 No change or Hold IT2001PA Engineering Essentials (2/2) 25
  • 26. Chapter 12 - Flip FlopSymbol SET Normal S Q INPUTS ACTIVE FF OUTPUTS HIGH R Q RESET Complementary SET input set Q-output with a binary ‘1’. RESET input reset Q-output with a binary ‘0’. IT2001PA Engineering Essentials (2/2) 26
  • 27. Chapter 12 - Flip FlopAdvantages of synchronous over asynchronousoperation FF outputs change in orderly manner. Everything in the system happens at the same time. IT2001PA Engineering Essentials (2/2) 27
  • 28. Chapter 12 - Flip FlopAsynchronous Inputs Symbol +5V PRE Preset & Clear inputs J Q • not triggered by clock pulses. CLK K Q CLR IT2001PA Engineering Essentials (2/2) 28
  • 29. Chapter 12 - Flip FlopAsynchronous Inputs Truth Table Preset Clear FF response 1 1 Normal clocked operation. Q will respond to J,K & CLK 0 1 Preset state, Q =1 1 0 Clear state, Q = 0 0 0 Prohibited IT2001PA Engineering Essentials (2/2) 29
  • 30. Chapter 12 - Flip FlopTiming diagram 1 J,K 1 CLK 0 1 PRE 0 1 CLR 0 1 Q 0 a b c d e f g IT2001PA Engineering Essentials (2/2) 30
  • 31. Chapter 12 - Flip FlopOperation Point Operation a Synchronous toggle on NGT of CLK b Asynchronous set on PRE = 0 c Synchronous toggle d Synchronous toggle e Asynchronous clear on CLR = 0 f CLR over-rides the NGT of CLK g Synchronous toggle IT2001PA Engineering Essentials (2/2) 31
  • 32. Chapter 12 - Flip FlopT Flip-Flops The T flip-flop is also J Q called toggle flip-flop. T K Q It can be easily implemented by High tying the JK inputs of the JK FF to high as J Q shown. CLK T K Q IT2001PA Engineering Essentials (2/2) 32
  • 33. Chapter 12 - Flip FlopT Flip-Flops Truth table Q Qn Clk Qn+1 T 0 1 Q 1 1 1 0 0 0 IT2001PA Engineering Essentials (2/2) 33
  • 34. Chapter 12 - Flip FlopT Flip-Flops Wave format T input Q T Q Wave form at Q output fo = 1/2 fin fo : Output frequency at Q fin : Input frequency at T IT2001PA Engineering Essentials (2/2) 34
  • 35. Chapter 12 - Flip FlopNext Lesson IT2001PA Engineering Essentials (2/2) 35