It's my first time to design the micro SD reader circuit. I hope that my design can support micro SD card with various speed class(from class2 to class10). According to my understanding, the only difference for different speed class is the clock frequency from a circuit perspective. Does my guess correct? Or are there other things should be concern about when designing a circuit for various speed class? Since the clock source is the CPU peripheral interface in my design, so if I don't change the clock frequency, does a class2 card has the same data rate as a class10 card?

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    \$\begingroup\$ How to design SD card reader? You should start with SD specifications and follow their physical layer recommendations... \$\endgroup\$ – Ale..chenski Jun 5 at 2:20
  • \$\begingroup\$ @Ale..chenski The CPU I use has an SDIO interface which I can connect to the SD socket directly. The thing I'm curious about is how to support various speed class. I mean should I design the circuit to match different speed class or the CPU can do it by itself. In its document, this part doesn't describe specifically. \$\endgroup\$ – Ross Jun 5 at 2:27
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    \$\begingroup\$ All SD cards respond at the slowest speed. Once you read the characteristics/speed from the device you configure your interface to suit. Clock speed and lanes used are selected based on the characteristics to get the best performance from each device. Start reading the specs here: sdcard.org/downloads/pls \$\endgroup\$ – Jack Creasey Jun 5 at 3:00

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