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Ian_Maw's avatar
Ian_Maw
Icon for New Contributor rankNew Contributor
2 days ago

Cyclone V SE Pulldowns on QSPI I/F. Why?

Hi guys.

I found an old adapter board which breaks out the JTAG, QSPI and configuration memory interfaces so that they can be connected to with standard connectors as the board is too small for these connectors to be provided.

There are 200R pulldown resistors on the four QSPI data bus signals and also on the clock signal. 

Has anyone else come across this? Do you know what it is for?

Thanks,

Ian

Configuration

2 Replies

  • FakhrulA_altera's avatar
    FakhrulA_altera
    Icon for Regular Contributor rankRegular Contributor
    1 hour ago

    Hi Ian,
     

    The 200 Ω pull-down resistors are not a general Cyclone V SE QSPI interface requirement. They appear to be a board-specific choice, likely to keep the connector-exposed QSPI signals at a defined low state and improve signal behavior when the external interface is disconnected.
     

    For a standard QSPI connection, the Cyclone V Pin Connection Guidelines specify the following for QSPI_CLK: use a series termination resistor near the SoC device-50 Ω for a single-memory topology, or 25 Ω for other topologies. The guideline does not specify 200 Ω pull-down resistors on QSPI_CLK or QSPI_IO[0:3].

    Reference: Cyclone V Device Family Pin Connection Guidelines (PCG-01014-3.2).
     

    Because 200 Ω is a relatively strong load, we do not recommend adding these resistors to a new design unless they are required by the specific board topology and have been validated.

     

    Best regards,
    Fakhrul