SD Card Transfer Mode

The SD card supports three transfer modes: SPI mode (independent serial input and serial output), 1-bit SD mode (independent command and data channels, unique transfer format), 4-bit SD mode (using extra pins and some Reset pins. Supports four-bit wide parallel transfers).

Low-speed cards usually support 0~400 kbit/s data transfer rates, using SPI and 1-bit SD transfer modes. The high-speed card supports 0~100 Mbit/s data transfer rate, using 4-bit SD transfer mode; supports 0–25 Mbit/s, using SPI and 1-bit SD mode.

There is an SD/SDIO license fee of $1,000 per year plus a $1,500 membership fee for manufacturers, sellers, and host adapter manufacturers. However, there is no licensing fee for SDIO card and MMC adapter manufacturers. The MMC card uses a 7-pin interface, and the SD card and SDIO card use a 9-pin interface.