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I am using Elm-chan FatFs module. I ported it correctly as it works when using a 16GB SD card. But when using a 32GB card, the code is getting stuck at the CMD55, ACMD41 set up loop.

Bellow is the print out of the command and response I am experiencing

cmd0, resp = 0x01
cmd8, resp = 0x01
cmd55, resp = 0x01
cmd41, resp = 0x01
cmd55, resp = 0x7F
cmd55, resp = 0x7F
cmd55, resp = 0x7F
cmd55, resp = 0x7F
cmd55, resp = 0x7F
cmd55, resp = 0x7F
cmd55, resp = 0x7F
cmd55, resp = 0x7F
cmd55, resp = 0xFF
cmd55, resp = 0xFF

Then from there, cmd55 always gets a response of 0xFF indefinitely. I've looked at other questions, spi SDC guides, and other ff.c implementations, and I am for the most part following it, because the code does work for a 16GB card, just when I switch to a 32GB card and restart the code, the 32GB card does not initialize.

Does it matter on the brand? the 32GB card is a samsung evo select micro sdhc. The 16GB is a Lexar micro sdhc

Emil
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1 Answers1

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It is not clear in your question which bytes are sent and which are received. Also you list different bytes in the question title that are not in the question body. Perhaps if you edit it then someone will be able to give you a better answer.

The response 0x80 to CMD55 means the card is not ready for the next command. After sending CMD55 you have to read bytes repeatedly in a loop until the most significant bit is clear. Only after that can you send the ACMD.

Tom V
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  • Thank you for the suggestion. For the CMD55, should it continuously read the SPI bus until 0x80 clears without re-sending CMD55 again? – Emil Oct 15 '21 at 02:40
  • Yes, send the command once, then just keep sending 0xFF (no command) while you read the response. Once you get a response where the top bit is zero that is your response to CMD55. Next you can send ACMD41, and again you have to read in a loop until the response comes. – Tom V Oct 15 '21 at 06:58
  • If this answer has helped you to make progress then can you please accept the answer with the tick mark on the left? thanks. – Tom V Oct 15 '21 at 13:04
  • Went through with your suggestion and confirmed that my code is still working. the 16GB sdcard works with expected behavior, a 32GB card does not work still. – Emil Oct 16 '21 at 01:10
  • New development, cmd55 is getting a response of 0x00 and gets stuck after that – Emil Oct 16 '21 at 02:14
  • I'm not sure if all new cards are required to support SPI mode any more. I no longer work at a company which is a member of the SD association, so I cannot get access to the latest version of the specifications. – Tom V Oct 16 '21 at 11:55
  • That is an interesting thing to know, I'll look into that. Thank you for your help! – Emil Oct 20 '21 at 21:51