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

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

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

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

Types Most basic, SR type:

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

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

D Type Flip Flop

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

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.