//-------------------------------------------------------------------------
向SD卡中写入命令，并返回回应的第二个字节
//-------------------------------------------------------------------------
unsigned char Write_Command_SD(unsigned char *CMD)
{
    unsigned char tmp;
    unsigned char retry = 0;
    unsigned char i;
    //禁止SD卡片选
    SPI_CS = 1;
    //发送8个时钟信号
    Write_Byte_SD(0xFF);
    //使能SD卡片选
    SPI_CS = 0;
    //向SD卡发送6字节命令
    for (i = 0; i < 0x06; i++) {
        Write_Byte_SD(*CMD++);
    }

    //获得16位的回应
    Read_Byte_SD(); //read the first byte,ignore it.
    do {
        //读取后8位
        tmp = Read_Byte_SD();
        retry++;
    }
    while ((tmp == 0xff)& & (retry < 100));
    return (tmp);
}

//----------------------------------------------------------
初始化SD卡到SPI模式
//----------------------------------------------------------
unsigned char SD_Init()
{
    unsigned char retry, temp;
    unsigned char i;
    unsigned char CMD[] = {0x40, 0x00, 0x00, 0x00, 0x00, 0x95};
    SD_Port_Init(); //初始化驱动端口

    Init_Flag = 1; //将初始化标志置1
    for (i = 0; i < 0x0f; i++) {
        Write_Byte_SD(0xff); //发送至少74个时钟信号
    }

    //向SD卡发送CMD0
    retry = 0;
    do {
        //为了能够成功写入CMD0,在这里写200次
        temp = Write_Command_SD(CMD);
        retry++;
        if (retry == 200) {
            //超过200次
            return (INIT_CMD0_ERROR); //CMD0 Error!
        }
    }
    while (temp != 1); //回应01h，停止写入

    //发送CMD1到SD卡
    CMD[0] = 0x41; //CMD1
    CMD[5] = 0xFF;
    retry = 0;
    do {
        //为了能成功写入CMD1,写100次
        temp = Write_Command_SD(CMD);
        retry++;
        if (retry == 100) {
            //超过100次
            return (INIT_CMD1_ERROR); //CMD1 Error!
        }
    }
    while (temp != 0); //回应00h停止写入

    Init_Flag = 0; //初始化完毕，初始化标志清零

    SPI_CS = 1; //片选无效
    return (0); //初始化成功
}

//------------------------------------------------------------
读取SD卡的CID寄存器   16字节   成功返回0
//------------------------------------------------------------
unsigned char Read_CID_SD(unsigned char *Buffer)
{
    //读取CID寄存器的命令
    unsigned char CMD[] = {0x4A, 0x00, 0x00, 0x00, 0x00, 0xFF};
    unsigned char temp;
    temp = SD_Read_Block(CMD, Buffer, 16); //read 16 bytes
    return (temp);
}

//-------------------------------------------------------------------
读SD卡的CSD寄存器   共16字节    返回0说明读取成功
//-------------------------------------------------------------------
unsigned char Read_CSD_SD(unsigned char *Buffer)
{
    //读取CSD寄存器的命令
    unsigned char CMD[] = {0x49, 0x00, 0x00, 0x00, 0x00, 0xFF};
    unsigned char temp;
    temp = SD_Read_Block(CMD, Buffer, 16); //read 16 bytes
    return (temp);
}

4） 读取SD卡信息
综合上面对CID与CSD寄存器的读取，可以知道很多关于SD卡的信息，以下程序可以获取这些信息。如下：
//----------------------------------------------------------------------
//返回
//  SD卡的容量，单位为M
//  sector count and multiplier MB are in
u08 == C_SIZE / (2 ^ (9 - C_SIZE_MULT))
//  SD卡的名称
//----------------------------------------------------------------------
void SD_get_volume_info()
{
    unsigned char i;
    unsigned char c_temp[5];
    VOLUME_INFO_TYPE SD_volume_Info, *vinf;
    vinf = &
    SD_volume_Info; //Init the pointoer;
    / 读取CSD寄存器
    Read_CSD_SD(sectorBuffer.dat);
//获取总扇区数
    vinf->sector_count = sectorBuffer.dat[6] & amp;
    0x03;
    vinf->sector_count <<= 8;
    vinf->sector_count += sectorBuffer.dat[7];
    vinf->sector_count <<= 2;
    vinf->sector_count += (sectorBuffer.dat[8] & amp; 0xc0) >> 6;
// 获取multiplier
    vinf->sector_multiply = sectorBuffer.dat[9] & amp;
    0x03;
    vinf->sector_multiply <<= 1;
    vinf->sector_multiply += (sectorBuffer.dat[10] & amp; 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;

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 & amp; 0xFF000000) >> 24 );
    CMD[2] = ((sector & amp; 0x00FF0000) >> 16 );
    CMD[3] = ((sector & amp; 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; j < Bytes; j++)
        *buffer++ = Read_Byte_SD();
}

//-----------------------------------------------------------------
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 & amp; 0xFF000000) >> 24 );
    CMD[2] = ((addr & amp; 0x00FF0000) >> 16 );
    CMD[3] = ((addr & amp; 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; i < 100; 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; i < 512; i++) {
        Write_Byte_MMC(*Buffer++);
    }
    //CRC-Byte
    Write_Byte_MMC(0xFF); //Dummy CRC
    Write_Byte_MMC(0xFF); //CRC Code


    tmp = Read_Byte_MMC(); // read response
    if ((tmp & amp; 0x1F) != 0x05) { // 写入的512个字节是未被接受
        SPI_CS = 1;
        return (WRITE_BLOCK_ERROR); //Error!
    }
    //等到SD卡不忙为止
//因为数据被接受后，SD卡在向储存阵列中编程数据
    while (Read_Byte_MMC() != 0xff) {};

    //禁止SD卡
    SPI_CS = 1;
    return (0); //写入成功
}