SD卡内部构造与工作原理

if(retry==100) //重试100次 {

SD_Disable(); //关片选

return(INIT_CMD1_ERROR); //如果重试100次失败返回错误号 }

}while(temp!=0);

MSD_Disable(); //关片选

SPCR=0x50; //设置SPI为2分频。进行高速读写 SPSR=0x01;

return(TRUE); //返回成功 }

//**************************************************************************** //发送命令给 MMC/SD卡

//Return: 返回MMC/SD卡对命令响应的第2字节，作为命令成功判断

unsigned char Write_Command_SD(unsigned char cmd,unsigned long address)

//**************************************************************************** {

unsigned char tmp; unsigned char retry=\

SD_Disable();

SPI_TransferByte(0xFF);

SD_Enable();

SPI_TransferByte(cmd); //将32位地址进行移位作为地址字节 SPI_TransferByte(address>>24); SPI_TransferByte(address>>16); SPI_TransferByte(address>>8); SPI_TransferByte(address); SPI_TransferByte(0xFF);

SPI_TransferByte(0xFF); do{

tmp = SPI_TransferByte(0xFF); //发送8个时钟接受最后一个字节 retry++;

}while((tmp==0xff)&&(retry<8)); return(tmp); }

//****************************************************************************

//写一个扇区(512Byte) to MMC/SD-Card //如果写完成返回TRUE

unsigned char SD_write_sector(unsigned long addr,unsigned char *Buffer)

//**************************************************************************** {

unsigned char temp; unsigned int i;

SPI_TransferByte(0xFF); //延迟8个时钟

SD_Enable(); //开片选

temp

Write_Command_MMC(MMC_WRITE_BLOCK,addr<<9); 送写扇区命令 if(temp != 0x00) {

SD_Disable(); return(temp); }

SPI_TransferByte(0xFF); SPI_TransferByte(0xFF); SPI_TransferByte(0xFE);

for (i=0;i<512;i++) {

=

//发 SPI_TransferByte(*Buffer++); //发送512字节数据 }

//CRC-Byte

SPI_TransferByte(0xFF); //Dummy CRC SPI_TransferByte(0xFF); //CRC Code

temp = SPI_TransferByte(0xFF); //读SD卡运行响应

if((temp & 0x1F)!=0x05) //如果最后4位为0101，为操作成功。否则为操作失败。 {

SD_Disable();

return(WRITE_BLOCK_ERROR); //返回错误 }

while (SPI_TransferByte(0xFF) != 0xFF);

SD_Disable();

return(TRUE); //返回成功 }

//**********************************************************