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I am trying to interface a MCU to an external non-volatile memory. The MCU being considered is TM4C123GH6. The memory selected is an SD card which is interfaced via SPI.

But the environment is a high vibration one which may cause the card to be dislodged. The other option could be eMMC. But are there MCUs with eMMC interfaces ? Any suggestions ?

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To answer your question: "are there?"... Yes! For YOU I would recommend using a TM4C123GH6.... (even if I've never heard of that processor :-) )

MMC is a way to talk SPI-like to memory cards. SD expands on that with some "secure" stuff that nobody uses. So your SD card is essentially an MMC card. Now when you lose the connector and solder the actual chip to the PCB, it is suddenly called eMMC. But in reality nothing is different from the SD card you were using before.

Modern eMMC memories do expand on MMC and SD a bit: they might offer a wider databus than the single serial channel for the oldfashioned MMC protocol. But if you don't need the speed, you can stick with the single data-bit protocol.

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eMMC has the same electrical interface as an SD card or MMC card. It can be either SPI or SDIO.

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  • The SPI mode of MMC and SD cards and eMMC modules is compatible. There is an open documentation of the eMMC standard, and some simplified documentation of the SD standard.

  • Latest revisions of the eMMC standard obsoletes this old SPI mode, but it is still very likely supported in all currently available modules.

  • In the native mode (CMD/CLK/DATA0..3), SD and MMC modules and cards have incompatible initialization sequences, likely for licensing reasons (MMC is free, SD is not). After initialization, MMC and SD can be compatible, but standards diverged at some time (8bits MMC vs. SD ultra modes...)

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