SD卡在单片机系统上的应用

Read_CSD_SD(sectorBuffer.dat);

//获取总扇区数

vinf->sector_count = sectorBuffer.dat[6] 0x03;

vinf->sector_count = 8;

vinf->sector_count += sectorBuffer.dat[7];

vinf->sector_count = 2;

vinf->sector_count += (sectorBuffer.dat[8] 0xc0) >> 6;

// 获取multiplier

vinf->sector_multiply = sectorBuffer.dat[9] 0x03;

vinf->sector_multiply = 1;

vinf->sector_multiply += (sectorBuffer.dat[10] 0x80) >> 7;

//获取SD卡的容量

vinf->size_MB = vinf->sector_count >> (9-vinf->sector_multiply);

// get the name of the card

Read_CID_SD(sectorBuffer.dat);

vinf->name[0] = sectorBuffer.dat[3];

vinf->name[1] = sectorBuffer.dat[4];

vinf->name[2] = sectorBuffer.dat[5];

vinf->name[3] = sectorBuffer.dat[6];

vinf->name[4] = sectorBuffer.dat[7];

vinf->name[5] = 0x00; //end flag

}

以上程序将信息装载到一个结构体中，这个结构体的定义如下：

typedef struct SD_VOLUME_INFO

{ //SD/SD Card info

unsigned int size_MB;

unsigned char sector_multiply;

unsigned int sector_count;

unsigned char name[6];

} VOLUME_INFO_TYPE;

5） 扇区读

扇区读是对SD卡驱动的目的之一。SD卡的每一个扇区中有512个字节，一次扇区读操作将把某一个扇区内的512个字节全部读出。过程很简单，先写入命令，在得到相应的回应后，开始数据读取。

扇区读的程序例程：

C程序

unsigned char SD_Read_Sector(unsigned long sector,unsigned char *buffer)
{ 
 unsigned char retry;
 //命令16
 unsigned char CMD[] = {0x51,0x00,0x00,0x00,0x00,0xFF};
 unsigned char temp;
 //地址变换 由逻辑块地址转为字节地址
sector = sector  9; //sector = sector * 512
    CMD[1] = ((sector  0xFF000000) >>24 ); 
    CMD[2] = ((sector  0x00FF0000) >>16 ); 
    CMD[3] = ((sector  0x0000FF00) >>8 ); 
 //将命令16写入SD卡
    retry=0; 
 do 
{ //为了保证写入命令 一共写100次
        temp=Write_Command_MMC(CMD); 
        retry++; 
 if(retry==100)
        { 
 return(READ_BLOCK_ERROR); //block write Error!
        } 
    } 
 while(temp!=0);
 //Read Start Byte form MMC/SD-Card (FEh/Start Byte)
 //Now data is ready,you can read it out.
 while (Read_Byte_MMC() != 0xfe);
    readPos=0; 
SD_get_data(512,buffer) ; //512字节被读出到buffer中
 return 0;
} 
其中SD_get_data函数如下： 
//---------------------------------------------------------
获取数据到buffer中 
//---------------------------------------------------------
void SD_get_data(unsigned int Bytes,unsigned char *buffer)
{ 
 unsigned int j;
 for (j=0;jBytes;j++)
    *buffer++ = Read_Byte_SD(); 
} 

6） 扇区写

扇区写是SD卡驱动的另一目的。每次扇区写操作将向SD卡的某个扇区中写入512个字节。过程与扇区读相似，只是数据的方向相反与写入命令不同而已。

扇区写的程序例程：

C程序

//-----------------------------------------------------------------
写512个字节到SD卡的某一个扇区中去  返回0说明写入成功 
//-----------------------------------------------------------------
unsigned char SD_write_sector(unsigned long addr,unsigned char *Buffer)
{ 
 unsigned char tmp,retry;
 unsigned int i;
 //命令24
 unsigned char CMD[] = {0x58,0x00,0x00,0x00,0x00,0xFF};
addr = addr  9; //addr = addr * 512
    CMD[1] = ((addr  0xFF000000) >>24 ); 
    CMD[2] = ((addr  0x00FF0000) >>16 ); 
    CMD[3] = ((addr  0x0000FF00) >>8 ); 
 //写命令24到SD卡中去
    retry=0; 
 do 
{ //为了可靠写入，写100次
        tmp=Write_Command_SD(CMD); 
        retry++; 
 if(retry==100)
        { 
 return(tmp); //send commamd Error!
        } 
    } 
 while(tmp!=0);
 //在写之前先产生100个时钟信号
 for (i=0;i100;i++)
    { 
        Read_Byte_SD(); 
    } 
 //写入开始字节
    Write_Byte_MMC(0xFE); 
 //现在可以写入512个字节
 for (i=0;i512;i++)
    { 
        Write_Byte_MMC(*Buffer++); 
    } 
 //CRC-Byte
Write_Byte_MMC(0x