说明：  spi 翻译资料 7.2 SPI总线 SD卡信道由指令和数据位（起始位和结束位）组成，SPI信道由字节定向。 每一个指令或数据块由8位的字节和CS标志构成。类似SD卡协议, SPI通讯由 指令、响应和数据组成。全部的主机与SD卡之间的通信由主机控制。主机执行 每一跟CS标志为低的总线
(spi Translation 7.2 SPI bus data channel from the SD card command and data bit (start bit and end bit) component, SPI channel directed by byte. Every command or data block from 8-bit bytes and CS constitute signs. SD card similar to the agreement, SPI communications from command, response and data components. All of the host and the communications between the SD card by the host control. Each host implementation with CS low marks for bus)