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Ophir_eng's avatar
Ophir_eng
Icon for New Contributor rankNew Contributor
7 months ago

Weak pull-ups \ tri-state at cyclone v soc

Hello, we are doing a bring up for a new card, we are seeing a phenomenon and trying to understand it, the fpga is loaded by the hps, and the nconfig pin is held constant at a logical 1, when the card is turned on, some of the pins go up to a logical 1 (before and during the firmware loading by the hps). We have an external pulldown of 10k (we get a voltage of 1 volt on this resistor), I wonder what is causing this phenomenon, is it necessary to change nconfig so that we do not boot with a weak pull up ?(we are interested in tri-state)
Fpga Devkit

4 Replies

  • FvM's avatar
    FvM
    Icon for Super Contributor rankSuper Contributor
    7 months ago
    • Hi,
      connecting 10k pull-down to nconfig isn't correct. The pin should have a pull-up resistor and temporarily pulled down to trigger reconfiguration.
    • Ophir_eng's avatar
      Ophir_eng
      Icon for New Contributor rankNew Contributor
      7 months ago
      Hi, thanks you for the comment

      We have constant pull-up on nconfig so nconfig always at high position

      Some of our outpus with pull down (to make sure that the en of the power supply will be at low position until the fpga will power up and enable the power supplies according our sequence), we saw at the oscilloscope that the en assert to high to 2-3 sec and then goes low
  • AqidAyman_Altera's avatar
    AqidAyman_Altera
    Icon for Regular Contributor rankRegular Contributor
    7 months ago

    Hello,


    In the Cyclone V Pin Connection Guideline, it mentioned:


    When you use the nCONFIG pin in a passive configuration scheme, connect the pin directly to the

    configuration controller. When you use the nCONFIG pin in an AS configuration scheme, connect

    the pin through a 10-kΩ resistor tied to VCCPGM. When you do not use the nCONFIG pin, connect

    the pin directly or through a 10-kΩ resistor to VCCPGM.


  • AqidAyman_Altera's avatar
    AqidAyman_Altera
    Icon for Regular Contributor rankRegular Contributor
    6 months ago

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