Logic Gates

The Gates:

Basics:

  • Main use is in multi-input devices to decide when certain events have happened.
  • Can be used to make monostables, astables and bistables.
  • They have one or more inputs and one output and can have their functions described by truth tables.
    • Just because the gates below mainly have 2 inputs does not mean that they cannot have three or more.
  • But they are not always required since simple logic functions can be performed with everyday components too.
  • Output of logic gates is always known as Q.

NOT Gate:

 NOT Gate

  • This gate is high whenever it’s input is low and vice versa.
  • For this reason it is also known as an inverter.

AND Gate:

  • This gate only gives a high output when all inputs are high.
  • Commonly used as safety devices in electrical machinery such as washing machines and microwave ovens

ANDgate

 

system and

 

This systems approach (diagram) describes the circuit above which in turn describes the function of an AND gate.

AND Gate

OR Gate:

  • This gate gives a high output when 1 or more of the inputs are high.

ORgate

 

systemOR

This systems approach (diagram) describes the circuit above which in turn describes the function of an OR gate.

NAND Gate:

  • This gate is the inverse of the AND gate and so gives a high whenever all inputs are not high at the same time.

NAND Gate

NOR Gate:

  • This gate is the inverse of the OR gate and so gives a high whenever all inputs are low at the same time.

NOR Gate

XOR Gate:

  • This gate’s name literally stands for ‘exclusively OR’.
  • It gives a high output whenever the number of inputs that are high is greater than 1 but not equal to the total number of inputs.

XOR Gate

XNOR Gate:

  • This gate’s name literally stands for ‘exclusively not OR’.
  • It’s output is high whenever either all the inputs or high or when all the inputs are low.

XNOR Gate

Acknowledgements:

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