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Altera_Forum's avatar
Altera_Forum
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9 years ago

PLL Input for Cyclone V

Hi,

I had a problem with my design, so the only way to have a clock into my Cyclone V is to use a standard I/O, but i can't use this one in order to program my ALT PLL:

Error (11667): Input reference clock of fractional PLL pll2_GammaCam:inst5|pll2_GammaCam_0002:pll2_gammacam_inst|altera_pll:altera_pll_i|general[0].gpll~FRACTIONAL_PLL must originate from a clock pin

Warning (179010): Source I/O is not placed onto a dedicated REFCLK input pin

Info (179012): Refclk input I/O pad XTIN_USB is placed onto PIN_H16

If any of you have an idea to work with it, it would be great.

Thank you

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    9 years ago

    http://quartushelp.altera.com/14.0/mergedprojects/msgs/msgs/ecclk_pll_refclk_not_from_dedicated_refclk.htm

    As that is a hardware limitation of the routing inside the FPGA, I think you may be limited to two solutions.

    Admittedly, I doubt that either solution will make you happy.

    1) Re-spin the board

    2) Feed in the clock frequency you want instead of using a PLL. This may require a custom crystal oscillator.

    One last-ditch option would be to short between any unused clock-input pin and an adjacent unused GPIO pin.

    Then you can route your clock though the FPGA's logic fabric as an asynchronous signal, and out of that GPIO pin.

    Then your clock signal will go out, and then back in to the chip on a dedicated clock-input pin that can have a PLL associated with it.

    Check your schematic, and on Quartus's pin planner to see which pins might be suitable for this work-around.

    Good luck.