I am interfacing SD cards (1/2GB SD cards and 4GB SDHC cards from different manufactures) to a custom board in SPI mode and I am using a FATfs file system from elm-chan. I am able to write files and read files on the SD card. However I would like to know where can I get the information on the maximum clock frequency (I can drive my SPI bus) for the given SD card. I have seen that for some SD cards maximum speed was about 1.33MHz and for some 20MHz. I assumed this speed was in the CSD register (TAAC value, as the TRAN_SPEED was the same on all the cards set at 25Mhz). However I realized its not true. I would really appreciate if someone can share their knowledge on this. Thanks!
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Without a clear part number of the SD card, it is not feasible to find it. The probability of getting a correct answer is high only if you can share the exact details. I suggest you to check the specification thoroughly of the respective SD card for a quick answer. Can you confirm whether the observation done by you is different from the information provided in the specification ?
Karthik Balaguru
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