Data transfers in SD cards are CRC checked. In addition, the card will by default start in a 12.5MB/s mode at 3.3v, which is 25MHz per lane. That's not DC, but

Data transfers in SD cards are CRC checked. In addition, the card will by default start in a 12.5MB/s mode at 3.3v, which is 25MHz per lane. That's not DC, but it's definitely slow enough to run on some pretty dodgy wiring. It will only switch to higher speed modes if requested, and if it actually works (falling back to lower speeds otherwise).