SD CARDS-SPI MODEOffered by flash-based SD Memory cards.Select this interface during first reset command after power-up(CMD0) and cannot be changed after the part is powered on.Only a subset of SD standard commands allowed in this mode.The commands and functions in SD mode defined after the Version 2.00 are not supported in SPI mode. Performance decreases in this mode as comapred to the SD mode.

Three tokens:-#Command#Response#Data-blockAll communications started by host. It does so by pulling CS signal low.Card responds to the command.Additionally, every data block sent to the card during write operations will be responded with a data response token. In the case of a Standard Capacity Memory Card, a data block can be as big as one card write block and as small as a single byte. In case of SDHC and SDXC Cards, block length is fixed to 512 bytes. MODE SELECTION AND INITIALISATIONSD card is powered up in the SD mode.It will enter SPI mode if the CS signal is pulled low during the CMD0(Reset command).If it goes well card will respond with responce R1.CMD8(SEND_IF_COND)->to verify SD card interface operating condition.