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Question about SDMMC_DLEN register

Question asked by Yosuf Taraki on Jan 23, 2018
Latest reply on Jan 24, 2018 by Clive One

We are developing a new product using STM32F767 processor, with a microSD card for storing data.  Page 1472 of the Reference Manual (RM0410) contains a description of the SDMMC data length register (SDMMC_DLEN).  There is a cryptic note on this page that reads:


For an SDMMC multibyte transfer the value in the data length register must be between 1 and 512.


I am trying to understand the meaning of this sentence.  I have found that we can read up to 262144 bytes per transfer when reading from the SD card.  This corresponds to 512 sectors. I don't understand why we cannot read more than 262144 bytes per transfer, but am wondering if it is related to the note above.  I would appreciate any help on this question.