# 3. Logic gates and logic circuits

# Chapter Overview

- Different types of Logic Gate
- NOT
- OR
- NOR
- XOR (EOR)
- AND
- NAND

- Pastpaper Question

## 3.1 Different types of Logic Gate

**NOT GATE***An Inverter that only has one input, it reverses the logic state*

Truth Table

A | A‘ |
---|---|

0 | 1 |

1 | 0 |

**OR GATE***An OR gate can have two or more inputs. The output will be True if at least one input is true.*

Truth Table

A | B | A + B |
---|---|---|

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 1 |

**NOR GATE — An Universal logic gate***The reverse logic of OR gate*

Truth Table

A | B | (A + B)’ |
---|---|---|

0 | 0 | 1 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 0 |

**XOR(EOR) GATE***A circuit which will give a True output if either, but not both, of its two inputs, is True*

Truth Table

A | B | A ⊕ B |
---|---|---|

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 0 |

**AND GATE***The output will be True when both inputs are true*

Truth Table

A | B | A * B |
---|---|---|

0 | 0 | 0 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 1 |

**NAND GATE — An Universal logic gate***The reverse logic of AND GATE*

Truth Table

A | B | (A * B)’ |
---|---|---|

0 | 0 | 1 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 0 |