实验目的：学习SD卡的操作.系统设计1、SD卡采用SPI通信2、先往SD里顺序写入0-255共256个数据，然后再读回送数码管显示-Experimental Objective: To learn SD card operation. System Design 1, SD card using SPI communication 2, first write to the SD sequence of 0-255 where a total of 256 data, and then read