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Hexadecimal, simply referred to as Hex, is a base-16 number system.

Most modern day PLC/PAC's use the hexadecimal number system some where within their architecture. Some PLC/PAC require that some instruction parameters be entered in Hex.

Base-16 numbers can be written in two formats:

24_{16} or 24h

in ControlLogix: 16#24

Base-16 also means that there are 16 valid numbers. Starting with zero they are:

0, 1, 2, 3, 4, 5, 6, 7, 8, 9

A, B, C, D, E, F

Where:

A = 10, B = 11, C = 12, D = 13, E = 14, F = 15

- Question to Ponder and Research
- Why the switch to letters? Why not simply use the numbers 10 through 15?

- How many bits of binary does it take to represent all 16 digits of a hex number?
- The answer is that it takes 4-bits of binary to represent any hex digit. The following table shows the hex digits and the corrisponding 4-bit binary number.

Hex Number | 4-bit Binary |
---|---|

0 | 0000 |

1 | 0001 |

2 | 0010 |

3 | 0011 |

4 | 0100 |

5 | 0101 |

6 | 0110 |

7 | 0111 |

8 | 1000 |

9 | 1001 |

A (10) | 1010 |

B (11) | 1011 |

C (12) | 1100 |

D (13) | 1101 |

E (14) | 1110 |

F (15) | 1111 |

Each digit in a hexadecimal number has a weight Value. The weight of a hex digit is the base raised to the power of the digit position. The figure below depicts an example.

The PLC/PAC Tutorial ⇔ All rights reserved
⇔ Copyright © 2009

John G. (Skip) Todora ⇔ Late updated: November 11, 2009

John G. (Skip) Todora ⇔ Late updated: November 11, 2009