Article ID: 000084823 Content Type: Error Messages Last Reviewed: 09/30/2014

Error:<Altera_PLL variation file name>: The specified configuration causes Voltage-Controlled Oscillator (VCO) to go beyond the limit.

Environment

  • Quartus® II Subscription Edition
    • BUILT IN - ARTICLE INTRO SECOND COMPONENT
    Description

    Due to a problem in the Quartus® II software version 12.1, you may see this error in the Altera_PLL MegaWizard™ Plug-In Manager when using the Enable physical output clock parameters option manually set your M and N counter values even though the VCO frequency should be within the supported operating range of the device. This problem occurs when generating an Altera_PLL with an M counter value greater than 255 and an N counter value of 1.

    Resolution

    If you require an M counter value of 256 or greater, and an N counter value of 1, you will need to perform the following steps in order to implement the desired setting for your Altera_PLL:

    1. Enter all of your desired parameters in the Altera_PLL megafunction with the following two exceptions:
      1. Enter a Reference Clock Frequency value equal to twice the value of your actual reference clock frequency.
      2. Enter a value of 2 for the Divide Factor (N-Counter).
        (By using the N value of 2 and a reference clock frequency twice of your actual clock frequency, the MegaWizard Plug-In Manager will be able to generate legal settings for the Altera_PLL).
    2. Create the megafunction variation file by clicking Finish.
    3. Open the <pll_name>_0002.v file created by the Altera_PLL MegaWizard Plug-In Manager.  This file is located in a sub-directory for your project in the <pll_name> folder.  Make the required modifications to the following parameters:
      1. Locate the .reference_clock_frequency parameter.  The value will be twice your desired clock frequency.  Modify the value to equal the actual reference clock frequency.
      2. Locate the .n_cnt_bypass_en parameter and change the value from "false" to "true".
    4. Save and close <pll_name>_0002.v.
    5. If you are going to perform functional simulations of the Altera_PLL megafunction, make the same parameter changes from step 3 above in the <pll_name>.vo file, located in the <pll_name>_sim folder in your project directory.

    This problem is scheduled to be fixed in a future version of the Quartus II software.

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