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We are designing a SD card interface with a processor.The processor supports SDR104 with clock frequency of 192MHz. Along similar lines,the UHS modes and corresponding clock frequencies mentioned are, SDR25 - 48 MHz ; SDR50 - 96 MHz ; DDR50 - 48 MHz ;

Don't we need at-least 208 MHz clock frequency to transfer 4 bit of data in SDR104 Mode(at 104MB/s) or about 50 and 100 MHz for SDR25/DDR50 and SDR50 modes? If the maximum achievable clock frequency is 192 MHz,are we still operating in SDR104 mode?

Please help me to understand these data rates and clock frequencies.

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SDR104 operating mode specifies various things, including

  • maximum power drawn by the card
  • communication voltage
  • maximum allowed clock speed

You can operate the interface at a lower clock speed, if you wish to do so, but you still need to meet the other requirements of SDR104 mode.

If you decide that 50MB/s is enough, you can design your system to meet the relaxed requirements of SDR50 mode. If you decide that you require 105MB/s, you need to choose the entirely different UHS-II mode.

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