Difference between microSD and SD protocols?

Discussion in 'Embedded Systems and Microcontrollers' started by Razor Concepts, Aug 6, 2010.

  1. Razor Concepts

    Thread Starter Active Member

    Oct 7, 2008
    212
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    Hi, I was just wondering if there was a difference between the SPI protocols with microSD and standard sized SD. Thanks!
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    What does the specification say? What spec you say. Well it's hard to answer such a question without a copy of the specification so tracking one down should be job #1
     
  3. Syniva

    New Member

    Jun 21, 2010
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    0
    I tried one once using one of those size-converting cards. Seems to work the same way.
     
  4. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    The difference is between SD and SDHC cards. It's easier to interface with SDHC cards because the data storage protocol is mainly block oriented vice byte for older SD cards.
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    Well even the SPI protocol on the SD Cards is Block Oriented so I'm not sure of the relevance of your comment. I think it would be helpful if the OP could articulate his requirements to a deeper level.
     
  6. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    Not really, at the SPI command level SD cards are byte addressed. Most drivers hide this fact at the routine interface level.
    SDHC cards can not be accessed to the byte level the way a SD card can unless you buffer an entire block.

    http://elm-chan.org/docs/mmc/mmc_e.html

    http://www.google.com/url?sa=t&source=web&cd=3&ved=0CBwQFjAC&url=http%3A%2F%2Fwww.freescale.com%2Ffiles%2Fmicrocontrollers%2Fdoc%2Fapp_note%2FAN3805.pdf&ei=d5JcTPLkIIXUtQPw89TUDQ&usg=AFQjCNHCKHHObB2FZu9Uzu5J6BUnLjr1Xg&sig2=v1edeSbbT17mOs8XnACf2A
     
    Last edited: Aug 6, 2010
  7. Papabravo

    Expert

    Feb 24, 2006
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    I see. So you say the SD Card is "byte addressed" because you can start a transfer at any byte location and read from 1 to N bytes where N may or may not have an upper limit.

    By comparison you seem to be saying that in the SDHC card you can begin only on a sector boundary and you must(?) read the entire sector.

    Did I get that right?
     
  8. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    That's it in a nut shell. For a SD card, N is up to 512 (BLOCK_LEN normally) but a SD cards (READ_BL_LEN) can be up to 2kBytes on large cards. This makes buffer size/capacity calculations a little more complex on a general SD card vs pure SDHC driver.

    http://en.wikipedia.org/wiki/SDHC#Compatibility_issues_with_4.C2.A0GB_and_larger_cards
    http://www.hjreggel.net/cardspeed/special-sd.html
     
  9. Vaughanabe13

    Active Member

    May 4, 2009
    102
    5
    SD and MicroSD are pin compatible. They are the same, just different physical sizes.
     
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