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Altera_Forum
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12 years ago

Be Warned: Altera FMC Connector not compatible with some daughter cards!

Hi - I was about to purchase an Arria V SoC Card to use with an ADI daughtercard (AD-FMCOMMS2-EBZ - demo card for the ADI 9361 ADC/DAC). However, it turns out the boards won't mate.

The Vita 57.1 standard that governs FMC connectors allows for a set of "user-defined" LVDS pairs. The standard says nothing about I/O direction. Xilinx LVDS I/O is bi-directional, but Altera LVDS I/O is not, and FPGA I/Os are assigned to these user-defined pairs in some arbitrary manner. The people at ADI used these user-defined pairs for all their I/O, and made their own choice about I/O direction, some of which conflict with the choices made by Altera. I don't know if ADI followed some informal sub-standard, or it was just bad luck. (Although if they had used the M2C/C2M pins which are specified for moving data, there wouldn't have been an issue). Still, if Altera is moving to full FMC support on their cards, it looks like they may have to also move toward bidirectional LVDS I/O.

So be warned! If you plan to buy an Altera board and use its FMC connectors, you need to explicitly check that it will work with your chosen DaughterCard.

/j

[Note - Altera devices do support "Emulated" LVDS which can convert LVDS inputs to "emulated" Outputs. This can help some, but performance is degraded (might be sufficient under a few hundred MHz, and it solves the problem only in one direction]

2 Replies

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

    thank you for this info.

    i am currently considering to buy this board.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    11 years ago

    Before purchasing a development kit combo; FMC carrier and FMC module, its important to create a spreadsheet to determine the pin compatibility between kits.

    Here's an example spreadsheet (Excel file in the .zip file) for a Texas Instruments TSW14J56 containing an Arria V GZ and a non-standard FMC connector (their documentation indicates that the connector assignments are "based on" the FMC specification), and a Vadatech FMC108 FMC-to-QSFP+ (which fully adheres to the FMC standard). To mate these two boards, I had to solder a number of jumper wires on the FMC108 board (testpoints existed on the board that I could access).

    Please use the attached spreadsheet as the basis for your own analysis. Please upload any spreadsheets you create to aid others.

    Cheers,

    Dave