Calculating Percentages in VHDL?

Discussion in 'VHDL' started by Cory Shol, Jan 22, 2014.

  1. Cory Shol

    Cory Shol Guest

    Hello all,

    I am working on a project that needs to complete safety crosschecks on a regular basis.

    If a User sets up the equipment at a specific setting the FPGA logic will calculate a Reference Voltage (lets say a 16 bit number ). The user will also set a percentage from 10-35% (Overvoltage Threshold).

    Once the user says he wants the system to allow 15% of overvoltage.

    I want to calculate in the logic the 16 bit referance voltage * .15 .

    How does one go about calculating percentages? I am using a Xilinx Spartan 3a 700a. A link to an tutorial or algorithm would be great.

    Cory Shol, Jan 22, 2014
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  2. Cory Shol

    Rob Gaddi Guest

    R * 0.15 = R * (0.15 * 2^17) / 2^17
    Rob Gaddi, Jan 22, 2014
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  3. Cory Shol

    Cory Shol Guest

    Ahh yes , I actually just thought about something similar to that just before I read the reply. Sometimes your brain doesn't work as fast as you want it to.
    Cory Shol, Jan 22, 2014
  4. Cory Shol

    Andy Guest

    Try the fixed point library in VHDL. It is included in the 2008 standard, and a quick google search will get you the vhdl fixed point user guide that shows you how to use it.

    Andy, Jan 22, 2014
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