SD卡读写实验程序

 return SPI2BUF;              //读取接收到的数据
}

    //*****************发送命令函数****************************
unsigned char SD_SendCommand(unsigned char cmd,unsigned long arg)
{
 unsigned char r1;
 unsigned char retry1=0;      //重复操作次数
 
 cs=0;                        //使能片选信号
 
 SPI_WriteByte(cmd | 0x40);  //分别写入命令
 SPI_WriteByte(arg>>24);      //数据段第4字节
 SPI_WriteByte(arg>>16);      //数据段第3字节
 SPI_WriteByte(arg>>8);      //数据段第2字节
 SPI_WriteByte(arg);          //数据段第1字节
 SPI_WriteByte(0x95);        //CRC效验和
 
 while((r1 = SPI_WriteByte(0xff)) == 0xff)//等待响应
  if(retry1++ > 200) break;//超时退出     
   
 cs=1;                        //清初片选信号

     return r1;                  //返回状态值
}

    //*******************SD开初始化函数**************************

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unsigned char sd_reset()
{
 unsigned char i,tmp;
 unsigned char retry;            //重复次数
 unsigned char r1=0;             
 retry=0;
 delay();
 delay();
 do
 {
        for(i=0;i<100;i++) SPI_WriteByte(0xff);
     
  r1 = SD_SendCommand(0,0);//发idle命令 
  retry++;
  if(retry>20) return 1;   //超时退出 
 } while(r1 != 0x01);      //等待IDLE命令返回

     

     retry = 0;                   
    cs=0;
  do
 {
        for(i=0;i<100;i++) SPI_WriteByte(0xff);

      r1 = SD_SendCommand(1, 0);         //发Active命令
  retry++;
  if(retry>254) return 1;            //超时退出
       } while(r1);  

        for(i=0;i<100;i++) SPI_WriteByte(0xff);

     r1 = SD_SendCommand(59, 0);            //关crc 
   if (r1) return 1;              //返回不正确，退出初始化

     for(i=0;i<100;i++) SPI_WriteByte(0xff);

        r1 = SD_SendCommand(16, 512);          //设扇区大小512
    if(r1!=0) return 1;                    //返回不正确，退出初始化
 return 0;                              //正常返回 
}

    //********************写一个扇区************************** 
unsigned char SD_WriteSingleBLOCk(unsigned long sector)
{
 unsigned char r1;
 unsigned int i;
    unsigned char retry=0;
 do
 {
        for(i=0;i<100;i++) SPI_WriteByte(0xff);

      r1 = SD_SendCommand(24, sector<<9);//写命令
  retry++;
  if(retry>10) return 1;             //超时退出 
 } while(r1 != 0x00); 

     cs=0;
 
 SPI_WriteByte(0xff);
 SPI_WriteByte(0xff);
 SPI_WriteByte(0xff);
 SPI_WriteByte(0xff);
 SPI_WriteByte(0xff);
 SPI_WriteByte(0xff);                 

     SPI_WriteByte(0xfe);                  //发开始符
 
 for(i=0; i<512; i++)                  //送512字节数据
 {
        if(i<255) SPI_WriteByte(i);       //发送0--255
  else SPI_WriteByte(512-i);        //发送255--0
        
 }
 
 SPI_WriteByte(0x95);
 SPI_WriteByte(0x95);                 //16-bits CRC

     r1 = SPI_WriteByte(0xff);            //读响应位
    if(retry++ >10) return 1;            //超时退出
    while(!((r1&0x0f)==5));              //等待数据成功接受返回信息
    while(!(SPI_WriteByte(0xff)));       //等待SD卡内部编程完成
  
 return 0;
}
     

    //******************读SD卡一个扇区************************
unsigned char SD_ReadSingleBlock(unsigned long sector)
{
 unsigned char r1,temp;
 unsigned int i,j;
 unsigned char retry=0;

     do
 {
  r1 = SD_SendCommand(17, sector<<9);//读命令
  retry++;
  if(retry>10) return 1;             //超时退出
 } while(r1 != 0x00); 
 cs=0;
 while(SPI_WriteByte(0xff)!= 0xfe)      //等待接收到开始字节
     {
       if(retry++ >100) return 1;          //超时退出
     }
 for(i=0; i<512; i++)                   //读512个数据
 {
  temp = SPI_WriteByte(0xff);        //读取接收到的数据
        LCD[0]=(temp/100)+48;
        lcd[1]=((temp%100)/10)+48;
        lcd[2]=((temp%100)%10)+48;
        lcd_display();                     //读取数据送显示

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本文关键字：程序  电脑-单片机-自动控制，电子学习 - 基础知识 - 电脑-单片机-自动控制