1. Lesson Objectives Aims
Use logic diagrams and truth tables – D type Flip Flops

2. It’s a white hole…
A flip flop is a circuit with 2 inputs…
…a pair of logic gates…
And the output of each gate feeds the input of the other

3. Latch or Delay They are used to: They can be called:
Remember a bit of information
Delay the progress of data (shift or rotate registers)
They can be called:
Latches
Delay
Data flip flop

4. The basic gist is you have a:
How do they work?
The basic gist is you have a:
Data line
Reset or Clock pulse
The circuit can then be activated “high” or “low”
Once a bit is “set” the data input makes no difference to the output of the circuit until the reset line is active again

5. Types
Most basic, SR type:

6. Problems with SR state
No control over the timing of the inputs
Can cause ambiguity of output if BOTH data and reset change at the same time

7. Beardy side note
Switches can bounce when pressed
This causes a series of 1,0 inputs instead of a single input
A flip flop can negate this effect to “smooth” the input

8. D Type Flip Flop

9. Have a look
Lets have a look at these circuits in a simulator to better understand how they work

10. Summary Flip flop circuits can be called delay, data or latch circuits
They are used to lock or remember a piece of data – 1 bit
They consist of a pair of gates which feed their outputs as inputs to the other gate
When controlled by a clock pulse there is no ambiguity
Usually made with NAND gates (which can mimic all other logic gates…)
When the clock is low, the data line has no effect.