51单片机实现对SD卡的读写
时间:11-25
来源:互联网
点击:
- PESD_volume_Info,*vinf;
- vinf=&SD_volume_Info;//Initthepointoer;
- /读取CSD寄存器
- 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);
- //getthenameofthecard
- 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;//endflag
- }
- 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:
- typedefstructSD_VOLUME_INFO
- {//SD/SDCardinfo
- unsignedintsize_MB;
- unsignedcharsector_multiply;
- unsignedintsector_count;
- unsignedcharname[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。
扇区读的时序:
扇区读的程序例程:
- unsignedcharSD_Read_Sector(unsignedlongsector,unsignedchar*buffer)
- {
- unsignedcharretry;
- //命令16
- unsignedcharCMD[]={0x51,0x00,0x00,0x00,0x00,0xFF};
- unsignedchartemp;
- //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);//blockwriteError!
- }
- }
- while(temp!=0);
- //ReadStartByteformMMC/SD-Card(FEh/StartByte)
- //Nowdataisready,youcanreaditout.
- while(Read_Byte_MMC()!=0xfe);
- readPos=0;
- SD_get_data(512,buffer);//512字节被读出到buffer中
- return0;
- }
- 其中SD_get_data函数如下:
- //----------------------------------------------------------------------------
- 获取数据到buffer中
- //----------------------------------------------------------------------------
- voidSD_get_data(unsignedintBytes,unsignedchar*buffer)
- {
- unsignedintj;
- for(j=0;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。
扇区写的时序:
扇区写的程序例程:
- //--------------------------------------------------------------------------------------------
- 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
- //--------------------------------------------------------------------------------------------
- unsignedcharSD_write_sector(unsignedlongaddr,unsignedchar*Buffer)
- {
- unsignedchartmp,retry;
- unsignedinti;
- //命令24
- unsignedcharCMD[]={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);//sendcommamdError!
- }
- }
- 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);//DummyCRC
- Write_Byte_MMC(0xFF);//CRCCode
- tmp=Read_Byte_MMC();//readresponse
- if((tmp&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
- }
此上内容在笔者的实验中都已调试通过。单片机采用STC89LE单片机(SD卡的初始化电压为2.0V
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