sd卡初始，由于SD卡使用SPI模式，并且是块读取(512Byte),所以需要单片机提供大于512的可用RAM，以供缓冲使用 这里可以选择STC89c52RD+、STC89C58RD+、STC89C516RD+，后缀RD+表明扩展RAM是1024字节，RC表明扩展RAM256字节-sd card original, because the SD card using SPI mode, and is a block read (512Byte), so they need the microcontroller to provide more than 512 of the available RAM, for buffer used here can choose STC89c52RD+, STC89C58RD+, STC89C516RD+, the suffix RD+ that extended RAM is 1024 bytes, RC that extended RAM256 byte