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Altera_Forum's avatar
Altera_Forum
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10 years ago

CYCLONE V OCT Problem

Hi,

I am using in my design a Cyclone V device (namely the 5CGXBC3B7U15C8N), while using PIN#M13, N12 as an LVDS RX port.

Going through ALTERA device handbook, it has two variations for On Chip Termination:

- Embedded inside FPGA.

- On board termination.

Does declaring LVDS inside QUARTUSII automatically attributes a 100ohm OCT for this pair?

Thank you for your answers,

Refael.

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    --- Quote Start ---

    The Cyclone V devices provide a 100 Ω, on-chip differential termination option on each differential receiver channel for LVDS standards. On-chip termination saves board space by eliminating the need to add external resistors on the board. You can enable on-chip termination in the Quartus Prime software Assignment Editor.

    --- Quote End ---

    By selecting LVDS you will automatically get the termination resistor. However, you can remove this by setting the 'Input Termination' to 'Off', or adding a line to the project's Quartus Settings File (.qsf):

    --- Quote Start ---

    set_instance_assignment -name INPUT_TERMINATION OFF -to your_input_signal

    --- Quote End ---

    Cheers,

    Alex
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    Hi Alex,

    Thank you for your reply.

    So, I receive differential termination by default, can I alter this value to a new value of my choosing?

    Also, currently in my design the RZQ resistor is not connected.

    From Altera's handbook I can see this resistor is used for calibration purposes, what is the termination value if this resistor is missing?

    Thanks,

    Refael.
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    You can adjust the On-Chip Termination (OCT) via this same 'Input Termination' parameter - various OCT options are available. However, I'm sure not all (if any) of the the OCT options will be valid for LVDS. I suspect you'll only be able to switch it OFF or leave it a it's default. Play around with it to see.

    --- Quote Start ---

    what is the termination value if this resistor is missing?

    --- Quote End ---

    Something that's not correct. The handbook doesn't cover this eventuality. Unfortunately, if you've not followed the guidelines, you're on your own. However,

    --- Quote Start ---

    Some specific DQ pins can also be used as RZQ pins. If you need extra RZQ pins, you can use these [the] DQ pins as RZQ pins instead.

    --- Quote End ---

    So, depending on your board you may be able to salvage something by using an alternative pin.

    Cheers,

    Alex