SDXC Card Initialisation with bare metal FPGA

Memory Cards SD | microSD | CFast | CFexpress | CompactFlash
1

Hello,
I am trying to use FPGA based SDXC card initialization and later data transfer.

I attempted to initialize SD card in a SD mode, and unable to get response from SD card post initiating ACMD41 command from FPGA Based design (Without processor). the SD card doesn’t assert response.

On a working SD card which was pre-formatted in a machine, we tried below sequence of commands through FPGA based Host controller while SD card is operating at on-board 3.3V power supply and SD clock during initialization was tried both 200KHz and 400KHz.

Command sequence (implemented):

  1. CMD0 (no response command, as per the specifications)
  2. CMD8 (received expected response from SD card (R7 Response - 0x08000001AA)
  3. CMD55 (Received expected response from SD Card (R1 Response – 0x3700000120)
  4. ACMD41(Received no response, we did tried multiple retries from Host controller however we are unable to receive ACMD41 response from SD card).

We are following below ACMD41 command format and retry mechanism as per the SD specification.

We tried below combinations of commands. (w/o CRC and End bit):

Attempt 1: 0x6951000100
Attempt 2: 0x6951000000
Attempt 3: 0x695100000F

Kindly let me know, if I am missing anything?

2

SDXC cards will be > 32GB so formatting with exFAT is the standard

3

Hi @gautamvsharma,
It looks like your initial sequence is mostly correct since CMD0, CMD8, and CMD55 are working. For ACMD41, make sure after CMD55, you immediately send ACMD41 without any delay. Also, double-check that the HCS (High Capacity Support) bit is set correctly in your ACMD41 argument, especially for SDXC cards (it should be set to 1). ACMD41 needs repeated retries every few milliseconds until the card is ready.

Also, confirm that your SD card’s voltage range matches (some newer SDXC cards prefer lower voltages like 1.8V). If available, try testing with an older SDHC card first to rule out compatibility issues.