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Altera_Forum's avatar
Altera_Forum
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18 years ago

DE boards, SD card hot-plug

SD/MMC cards are supposed to support hot-plug and live insertion. But I don't see any kind of protection on the SD connector. It is the same on all the Altera/Terasic DE boards.

I know the pins are arranged for the corrector contact order. But is this enough? Shouldn't be some diode protection on the board?

3 Replies

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

    Hello,

    from the MMC specification:

    --- Quote Start ---

    If hot insertion feature is implemented in the host, than the host has to withstand a shortcut between VDD and VSS without damage.

    --- Quote End ---

    With Terasic DE1 and DE2, VDD ist directly connected to 3.3V supply, I guess the quoted condition isn't met. You could conclude, that these Boards thus don't implement hot plugging. But I would worry about for a retail product, not for an evaluation board. I'm also in doubt, if typical consumer products care about MMC spec. For an industrial product, I would recommend a current limiter for VDD and protection diodes at data lines. I won't be sure, if e. g. supply contact lead is enough to prevent from ESD hitting a data line during card insertion.

    Regards,

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

    Thanks Frank,

    I also wonder what kind of protection consumer devices have. And I'm tempted to open a card reader to see what's in there.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    18 years ago

    Hello,

    card readers most likely utilize application specific devices that may have more effective internal protection than an FPGA.