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.

    Thanks
     
    Cory Shol, Jan 22, 2014
    #1
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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
    #3
  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
     
    Andy, Jan 22, 2014
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