**Overview of Digital Logic**

**Binary Logic:**

- Computer uses binary number system because the two voltage levels can be represented as the two digits 0 and 1.
- Signals in digital electronics have two distinct voltage levels.
- A system may define 0V as logic 0 and +5V as logic 1.

**Logic Gates:**

AND Logic:

AND Logic:

- And logic function will output a 1, if all or two of its input are 1.

Inputs | Output | |
---|---|---|

X | Y | X AND Y |

0 | 0 | 0 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 1 |

**OR Logic:**

- OR logic function will output a 1, if one or more inputs are 1.

Inputs | Output | |
---|---|---|

X | Y | X OR Y |

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 1 |

**XOR Logic:**

- Performs an exclusive OR operations on the input.
- Produces 1 output if only one input is 1.
- A way to remember XOR is "one or the other but not both".
- Can be used to compare two bits to see if they are the same.

Inputs | Output | |
---|---|---|

X | Y | X XOR Y |

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 0 |

**Buffer:**

- A buffer does not change the logic level of the input.
- Used to isolate or amplify the signal.

Inputs | Output |
---|---|

0 | 0 |

1 | 1 |

**NOT Logic:**

- NOT logic, also called Inverter, outputs the value opposite to that input to the gate.

Inputs | Output |
---|---|

X | NOT X |

0 | 1 |

1 | 0 |

**NAND Logic:**

- AND logic with an inverter on the output.

Inputs | Output | |
---|---|---|

X | Y | X NAND Y |

0 | 0 | 1 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 0 |

**NOR Logic:**

- OR logic with an inverter on the output.

Inputs | Output | |
---|---|---|

X | Y | X NOR Y |

0 | 0 | 1 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 0 |

**XNOR Logic:**

- XOR logic with an inverter on the output.

Inputs | Output | |
---|---|---|

X | Y | X XNOR Y |

0 | 0 | 1 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 1 |

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**Related topics:**

Microcomputer System | Microcomputer System Architecture | Numbering System | Memory Basics | ASCII Code | Computer Internals | ROM and RAM Memory

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