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adding a memory card to single-chip CPU

Discussion in 'Electronic Design' started by David Collier, Mar 13, 2006.

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  1. I'd like to add a removable memory card ( 128Mbytes or more I suppose )
    to my tentative design, which uses the AT91SAM7x128 processor. As far as
    I can see the processor has no in-built assistance for communicating
    with a CF, MMC/SD, smartmedia or any other external flash device I might

    In particular I can't instantly see that I can output a read or write
    strobe so I may have to bit-bash the whole dratted read and write
    cycle... though you may know better.

    I've designed ( on another project), but never built, a smartmedia
    interface, which requires about 12 pins. I could handle that, and I
    could use it for a soldered-on NAND flash if I liked too, so that's a

    I believe the MMC/SD card has a serial mode which looks a bit SPI-like,
    but I know nothing more about it. Anyone know if you can actually use
    all the memory over that interface? Is it SPI?

    The ideal would be a 2cm square device with a nice simple interface,
    which corresponds to a nice simple interface in the 7x CPU which I don't
    happen to be using. :)

    Anyone got any suggestions, or know of any Atmel/other application notes
    on the subject?

  2. John B

    John B Guest

    I have interfaced ATmega128 to SD memory cards with the built in SPI interface. It's very easy with
    a couple of caveats. Firstly SD is 3.3V so M128 signals have to be fed through a couple of
    resistors and secondly it is not possible to use the #CS pin of the SPI interface as the SD card
    pulls this line low to indicate its presence. You need to use another pin.

    Progressive resources have a useful FAT 16 library for M128 but I dont know if it is ported to the
    ARM yet. Have a look at
  3. Guest

    On Mon, 13 Mar 2006 11:16 +0000 (GMT Standard Time),
    Everyday Electronics starting May 2005 had a good article on how to
    talk to CF cards... they were ultimately looking to get a PIC talking
    to it so with some tweaks, it sounds right up your street.

  4. Tim Wescott

    Tim Wescott Guest

    Circuit Cellar covered this in detail a few months ago, using a 3-wire
    interface to memory cards.


    Tim Wescott
    Wescott Design Services

    Posting from Google? See
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