Initialization of a microSD card using an SPI interface

Question

I'm using a microSD card in an embedded design. The card is connected to a microcontroller using the SPI interface. It worked fine for all cards I've used before, but now my new card will not initialize. The card is a Transcend 2 GB microSD card (TS2GUSD).

After sending the initial clock train to switch to SPI mode, I do the following:

1. CMD0 (Argument 0, CRC 0x95) -> Response 0x01 -> OK

2. CMD8 (Argument 0x000001AA, CRC 0x87) -> Response 0x01 0x000001AA -> Means it's SDC V2+ card, the voltage range 2.7 V - 3.6 V is supported -> OK

Then I should send the ACMD41 command, but when sending the CMD55 (argument 0, CRC 0) that must precede CMD41, I get response 0x05 -> Illegal Command. I've also tried to send CMD1 (for MMC cards), but it gives a similar illegal command response. The code works fine with my Sandisk 2 GB microSD card.

How do I fix this problem?

Answer 1

I seem to have found the issue. When I calculate the correct CRC for CMD55 and send that instead of a dummy CRC, the command is accepted (result 0x01). If you look at the physical layer specification in section 7.2.2, it explicitly says that:

The SPI interface is initialized in the CRC OFF mode in default. (except for commands CMD0 and CMD8).

This doesn't seem to be the case with this series of Transcend cards, thus violating the specification. Also in case of a CRC error the reply should be 0x09 instead of 0x05. I've tried to explicitly turn off CRC checking with CMD59, but that doesn't seem to help.

=> Calculating the correct CRC for (all?) commands makes the card work.

I'm in contact with Transcend support about this. If I learn something useful I'll you know here.

Note that I used other 2 GB Transcend cards before, but they were made in Taiwan, while the new one is made in Korea (and seems to be a Samsung card (MMAGR02GUDCA)).