SD Voltages

I am reading a CPU eval board data sheet that says it supports 1.8 volt interface for MMC cards. They don't seem to support SD cards. Looking at wikipedia they say, "All SD card families initially use a

3.3-volt electrical interface. On command, SDHC and SDXC cards switch to 1.8-volt operation." How is that intended to work? I don't see the utility of requiring a voltage converter chip so you can first run at 3.3 volts then switch to 1.8 volts. Is this the only way to make this work if you don't want to have two types of cards? I guess I would have expected the interface to work from what ever voltage is present on the power pin, no?

So how is this used in a design typically? The CPU I am considering can only work with 1.8 volt I/Os. Do I really have to use a level shifter chip to complete this interface?


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Ask the manufacturer of the CPU eval board.

For HW design, just dump in a SN74AVC4T774 and be done with it.

Leo Havmøller.

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Leo Havmøller

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