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I am trying to read an microSD card through an unbranded SD slot and a Basys3 FPGA. The microSD card, Kingston microSD HC 8GB Class 4, is used via an SD card adapter, also Kingston.

I am having trouble with getting past CMD8 of the initialization process. After I sent CMD0 it responded with 0x01 which is normal. After CMD0 I sent the CMD8 command; it responded with 0x000000021F. I wasn't able to find anything related to this code in any documentation.

To test, I tried using a SanDisk Ultra SDHC 32GB Class 10 with the same code. It successfully initialized.

Other things I have tried:

Please help.

Waveforms

The first one shows all of the initialization process. SD_CD is Card Detect (Active Low) and SD_WP is Write Protect (Active Low). SD_CLK is running at 390 kHz, 256 times slower than _cpuClock. Please note that the SD_MISO, SD_CD, SD_WP and _cpuClock are all simulated manually (i.e. doesn't receive any signal from the SD module). After card is detected, 1 millisecond is waited, followed by 74 SD_CLK's.

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The second image is a zoom in of CMD0 and its response.

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The third image is a zoom in of CMD8 and its response.

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The final image is a zoom in of CMD55 and its response.

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Update 1 (Prior to @Annoymous Answer) I managed to get my hands on a couple more cards. After testing it seems that only SanDisk Class 10 SDHC (both SD and microSD) returns an initialization finished state. The Kingston Class 4 SDHC SD returns a timeout after CMD0 while the Kingston Class 4 SDHC microSD returns a 0x000000021F. Changing the adapter made no difference in all cases. In the image below, the successful ones are in green and the unsuccessful ones are in red.

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Update 2 (Response to @Annoymous Answer) After changing MOSI from posedge to negedge, the Kingston Class 4 SD card seems to initialized (which was previously timeouted). However, the Kingston Class 4 microSD card still respondsed with 0x000000021F.

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    \$\begingroup\$ Both are SDHC, right? Are they both capable of the same class of operation? Sounds like the adapter is the difference. Any other adapters handy? \$\endgroup\$
    – jonk
    May 21, 2017 at 20:49
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    \$\begingroup\$ Do you send enough dummy clocks prior to initialization? \$\endgroup\$
    – JimmyB
    May 21, 2017 at 21:00
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    \$\begingroup\$ @JimmyB I sent 74 clocks prior to initialization. I will update my answer with the simulated waveform. \$\endgroup\$
    – krismath
    May 21, 2017 at 21:04
  • \$\begingroup\$ @jonk I updated the class of each of the cards. Does class effects operation? I know that there are SDv1 and SDv2, but I am not aware how this is related to Class 4/Class 10. Regarding your other question, no other adapters are available. \$\endgroup\$
    – krismath
    May 22, 2017 at 11:26
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    \$\begingroup\$ @krismath I wish I were expert in any of this, but unfortunately I'm not. You probably know a fair bit more than I do. But sometimes it helps to hear someone else's thoughts and questions when tracking something like this, so I offered a few that came to mind. That's about my limit, though, without spending a lot more time getting up to speed. \$\endgroup\$
    – jonk
    May 22, 2017 at 17:52

1 Answer 1

Reset to default
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Attached CMD8 picture shows normal response 1AA (2.7 - 3.6 V, and check pattern AA).

Several notes on things I see:

  • do not start command immediately after you activate CS. Wait 8 spare clock cycles, and only then start the command;
  • same at the end. Do not deactivate CS just after you think you got complete response for the command. Perform 8 more spare clock cycles before you deactivate CS;
  • I am not sure but pictures show that you put data onto the SD-card inputs on positive edge of the SD-card clock. As I recall SD-card latches data on positive edge of its clock, thus putting data there at the same time may violate timing. In my implementation, if I recall properly, I put data onto SD-card input lines on negedge, so that it samples it on next posedge.
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  • \$\begingroup\$ Actually the CMD8 response was manually simulated -- this wasn't the actual SD's response. I will try what you suggested. Thanks! \$\endgroup\$
    – krismath
    May 22, 2017 at 9:53
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    \$\begingroup\$ Thanks, more cards seems to have initialized after posedge is set to negedge. More dummy clocks are next in list! \$\endgroup\$
    – krismath
    May 22, 2017 at 11:56
  • \$\begingroup\$ Unfortunately, after giving it more dummy clocks and setting CS according to you answer, the SD card still responds with 0x000000021F \$\endgroup\$
    – krismath
    May 22, 2017 at 18:48
  • \$\begingroup\$ Ok, then I would do the following: (1) did you check if this card is operational at all? Try it with windows or linux machine. I do not see it from your post; (2) take either real waveforms from the SD-card interface, or perform simulation to see the waveforms and timing of them towards the card. \$\endgroup\$
    – Anonymous
    May 22, 2017 at 19:07
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    \$\begingroup\$ It seems that while the 'faulty' card is operational on a standard, commercial microSD card reader, the card failed to operate in my situation. I am clueless and would probably leave it at that; however if anybody is interested in the code, please feel free to visit github.com/kkalavantavanich/SD2017 . \$\endgroup\$
    – krismath
    Jun 7, 2017 at 18:28

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