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MMC and SD what's the diff

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kar2on

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I was just wondering whether or not a piece of hardware setup to perform MMC read/writes would do the same for SD cards. I actually have a hardware setup to perform read/writes on MMC but when I plug in my SD nothing seems to happen, after a couple of card pulls and pushs I manage to get one sector to be written, according. According to the Sanddisk product manual a card operaing in SPI, the pins are pretty different, SD allocates the first 7 pins for SPI mode, these do not correspond to the 7 pins of a MMC card if the same socket is used.

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sorry after reading the specs again, I see that the pin assignments do match. But i'm still unable to perform a proper read/write cycle with my SD card.
 

scarecrow_here

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MMC (SPI) card has 1-bit interface and SD has 4-bit, so SD is faster than MMC. With SPI interface setting, SD is compatible with MMC. I guess you didn't set the SD card mode correctly. There is a control to select between SD or SPI. Check the enclosed SD spec.
 

kar2on

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I guess you're right, I'm using an SD card I got from a Canon camera , there seems to be a switch at the side of the card I didn't notice before... but even chaging the switch position doesn't get the card to work. I'll have to read through the specs before attempting this again. Thanx.
 

kar2on

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i've read through the specs (briefly) and noticed even in SPI mode, the SD card has an extra interrupt pin, a interrupt is triggered by asserting this pin to high, so I'm guessing normal operation would be to assert this pin to LOW... can anyone confirm this? If I have to assert pin 8 to LOW, then could I just tie it to GND together with pins 3 and 6, if I'm only gonna use MMC/SPI mode.
 

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