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Is possible with SDHC microSD card write 32 bytes of data without loading full block o the RAM? SDHC has for some operations fixed block size to 512 so I dont know if it is possible. If possible what commands I have to use? If it is not possible is another way to write data to SD card from MCU with <= 512B RAM?

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    \$\begingroup\$ IIRC older SD card format (size <=2GB) could support byte accesses. Can't you use this instead ? \$\endgroup\$
    – Grabul
    Commented Jun 19, 2018 at 20:52
  • \$\begingroup\$ What is the application? Is there some reason you might need to read data from the block before writing to it? \$\endgroup\$ Commented Jun 19, 2018 at 21:25
  • \$\begingroup\$ I want to overwrite 32B of block (512B). \$\endgroup\$
    – Misaz
    Commented Jun 20, 2018 at 5:32

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Is possible with SDHC microSD card write 32 bytes of data without loading full block o the RAM?

No. Partial block support was removed from the spec for SDHC.

Note that it was optional for SD, and many cards did not implement that feature at all.

Also note that RAM sizes for current generation MCUs are no longer that small.

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