4.3.9

Flip Flops

Test yourself

D Type Flip Flops

Flip flops are electronic circuits used within a computer’s memory to store single bits in one of two states, either a 1 or a 0. Flip flops can alter the state from one to the other.

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D type flip flops

  • There are several types of flip flop, but by far the most common are D type flip flops.
  • D type flip flops have two inputs:
    • Data, D.
    • A clock signal.
  • D type flip flops have one output, Q.
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Clock signal

  • The clock signal is a regular and steady pulse used by a CPU to time operations.
  • The output Q of a D type flip flop can only be altered at the beginning of a clock signal.
  • A change to Q will only occur if D is in a different state to what it was at the start of the previous clock signal.
  • This happens regardless of whether or not there has been a change in between clock signals.
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Signal diagram

  • The top line shows the data, D, alternating between 0 and 1 at random.
  • The middle line is the steady and regular pulse of the clock signal.
    • The start of each pulse identified with an arrow.
  • The bottom line is the output, Q.
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Process

  • At the first pulse, the output changes to ‘1’ to match D.
  • At the second pulse, D is still ‘1’ so Q doesn’t change.
  • At the third pulse, D is now ‘0’ so Q changes to ‘0’ at this point.
  • At the fourth pulse, D is back to ‘1’ so Q changes to match it.
    • The change in D in between clock pulses is ignored.

Jump to other topics

1Components of a Computer

2Software & Software Development

3Exchanging Data

4Data Types, Data Structures & Algorithms

5Legal, Moral, Cultural & Ethical Issues

6Elements of Computational Thinking

6.1Thinking Abstractly

6.2Thinking Ahead

6.3Thinking Procedurally

6.4Thinking Logically

6.5Thinking Concurrently

7Problem Solving & Programming

8Algorithms

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