Understanding Flip Flops

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Software Developers View of Hardware Understanding Flip-Flops

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Transcript of Understanding Flip Flops

  • 1. Software Developers View of Hardware Understanding Flip-Flops
  • 2. What is a Flip-Flop?
    • A flip-flop is a bistable device.
    • This means that output from the device can be one of two possible states and will remain that way even after input signals are removed.
    • A flip-flop will only change state when commanded.
    • Because of this they form the basis of memory.
  • 3. Components
    • A flip-flop has three (3) basic components:
      • Latch
      • Clock
      • Trigger
  • 4. Latches
    • The most basic of all latches is the RS latch.
    • There are TWO types of RS latches, they are:
    NOR Latch NAND Latch
  • 5. Latches
    • The basic understanding behind a latch is that if 1 is sent as the SET input then the output (Q) will be 1.
    • Likewise, if 1 is sent to the RESET input then the output (Q) will be 0.
    • The most important part is FEEDBACK which enables the latch to carry out the task of enabling memory.
  • 6. NOR Latch
    • Firstly, lets look at the RESET condition. (Send 1 as RESET input)
    1 0
  • 7. Look at the Truth!!!!!! 0 1 1 0 0 1 0 1 0 1 0 0 X B A
  • 8. Look at the Truth!!!!!! 0 1 1 0 0 1 0 1 0 1 0 0 X B A
  • 9. NOR Latch
    • So therefore, if an at least one input is a 1 then the only possible output can be 0.
    1 0
  • 10. NOR Latch
    • So therefore, if an at least one input is a 1 then the only possible output can be 0.
    1 0 0 0 1 1
  • 11. NOR Latch
    • Next, lets look at the SET condition. (Send 1 as SET input)
    0 1
  • 12. NOR Latch
    • Next, lets look at the SET condition. (Send 1 as SET input)
    0 1 0 0 1 1
  • 13. NOR Latch
    • Next, lets look at the HOLD condition. (Will hold what ever was the previous output)
    0 0 0 1
  • 14. NOR Latch
    • Next, lets look at the HOLD condition. (Will hold what ever was the previous output)
    0 0 0 1 0 1
  • 15. NOR Latches
    • This is where the see saw effect comes into play:
  • 16. NOR Latch
    • Finally, for a NOR latch when 1 and 1 are both entered this violates logic rules because Q and NOT Q cannot be the same.
    • It is referred to as being illegal.
  • 17. NOR Latch Truth Table
  • 18. NAND Latch
    • Firstly, lets look at the RESET condition. (Send 1 as RESET input)
    0 1
  • 19. Look at the Truth!!!!!! 0 1 1 1 0 1 1 1 0 1 0 0 X B A
  • 20. Look at the Truth!!!!!! 0 1 1 1 0 1 1 1 0 1 0 0 X B A
  • 21. NAND Latch
    • Firstly, lets look at the RESET condition. (Send 1 as RESET input)
    0 1 1 1 0 0
  • 22. NAND Latch
    • Next, lets look at the SET condition. (Send 1 as SET input)
    1 0 1 1 0 0
  • 23. NAND Latch
    • Next, lets look at the if 1 is sent to both inputs.
    0 1
  • 24. NAND Latch
    • A point to remember is that a NAND flip flop works oppositely to a NOR flip flop so an input of (0 0) is illegal. However, an input of (1 1) cause the gate to remember the previous input.
  • 25. NAND Latch
    • Next, lets look at the if 1 is sent to both inputs.
    1 1 What you will notice is that it depends on the see saw.
  • 26. NAND Latch
    • Next, lets look at the if 1 is sent to both inputs.
    1 1 What you will notice is that it depends on the see saw.
  • 27. NAND Latch
    • Next, lets look at the if 1 is sent to both inputs.
    1 1 What you will notice is that it depends on the see saw. 1 0
  • 28. NAND Latch
    • Complete the following truth table depending on the inputs shown.
    1 0 1 1 Q Q D C B A
  • 29. Clocked RS Latch
    • The logic behind this logic gate is the fact that there is another input called ENABLED.
    • This acts like a gate or a switch and when set to 1 the circuit will respond as usual. However, when it is set to zero the circuit will not respond.
  • 30. Clocked RS Latch
  • 31. Clocked RS Latch