Electrical – microSD Class 4 card in SPI mode returns 0x000000021F after `CMD8`

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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.

Best Answer

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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