51单片机读写SD卡程序

//================================================================
//往SD卡指定地址写数据,一次最多512字节
//unsigned char SdWriteBlock(unsigned char *Block, unsigned long address,int len)
unsigned char SdWriteBlock(unsigned long address,int len)
{
unsigned int count;
unsigned char dataResp;
//Block size is 512 bytes exactly
//First Lower SS
SD_CS=0;
//Then send write command
SdCommand(0x18,address,0xff);
if(SdResponse()==00)
{
SdWrite(0xff);
SdWrite(0xff);
SdWrite(0xff);
//command was a success - now send data
//start with DATA TOKEN = 0xFE
SdWrite(0xfe);
//now send data
//for(count=0;count for(count=0;count //for(count=0;count for(;count<512;count++) SdWrite(0);
//data block sent - now send checksum
SdWrite(0xff); //两字节CRC校验, 为0XFFFF 表示不考虑CRC
SdWrite(0xff);
//Now read in the DATA RESPONSE token
dataResp=SdRead();
//Following the DATA RESPONSE token
//are a number of BUSY bytes
//a zero byte indicates the MMC is busy
while(SdRead()==0);
dataResp=dataResp&0x0f; //mask the high byte of the DATA RESPONSE token
SD_CS=1;
SdWrite(0xff);
if(dataResp==0x0b)
{
//printf("DATA WAS NOT ACCEPTED BY CARD -- CRC ERROR");
return 0;
}
if(dataResp==0x05)
return 1;
//printf("Invalid data Response token.");
return 0;
}
//printf("Command 0x18 (Write) was not received by the MMC.");
return 0;
}
//=======================================================================
//从SD卡指定地址读取数据,一次最多512字节
unsigned char SdReadBlock(unsigned char *Block, unsigned long address,int len)
{
unsigned int count;
//Block size is 512 bytes exactly
//First Lower SS
//printf("MMC_read_block");
SD_CS=0;
//Then send write command
SdCommand(0x11,address,0xff);
if(SdResponse()==00)
{
//command was a success - now send data
//start with DATA TOKEN = 0xFE
while(SdRead()!=0xfe);
for(count=0;count for(;count<512;count++) SdRead();
//data block sent - now send checksum
SdRead();
SdRead();
//Now read in the DATA RESPONSE token
SD_CS=1;
SdRead();
return 1;
}
//printf("Command 0x11 (Read) was not received by the MMC.");
return 0;
}

void initbaud(void)
{
TMOD=0X20;
TH1=0XFD;
TL1=0XFD;
PCON=0X00;
TR1=1;
SCON=0X50;//8位波特可变
//SCON=0X52;//8位波特可变 TI开中断
}
//============================================================
//主程序
main()
{
unsigned int i;
unsigned long AddTemp=331264;//SD卡地址第一个数据物理地址初始值，可以用winhex查看，这里是641物理扇区，512x641=328192，根据实际SD卡内容更改
delayms(5);
SdInit();//SD卡初始化
while(1)
{
SdWriteBlock(AddTemp,512);
delayms(1000);
AddTemp=331264;
SdReadBlock(DATA,AddTemp,512);//每次读出512字节放到缓冲区
initbaud();
for(i=0;i<512;i++)
{
SBUF=DATA[i];
while(!TI);
TI=0;
delayms(1);
}
while(KEY);//等待按键按下继续执行

}
}
可以在串口中看到SD卡中被写入的数据，程序在MCU-51/AVR开发板进行了实验。具体介绍可访问：
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