SD cards are easily interfaceable with FPGAs. They come in different sizes (standard, mini and micro) but electrically they all work the same way. Let's focus on micro-SD cards since they are conveniently small and popular nowadays.
Micro-SD cards have 8 pins. First the power connection goes on pins 4 and 6.
Then, you need between three and six connections to FPGA pins depending on the mode of operation you decide to use.
The SPI mode is often used in microcontroller systems. With an FPGA, we migh be better served with the...
In SD modes, the CMD/DATx lines are bidirectional. That means:
So for example, we need these connections in SD one-bit mode: