单片机读写SD卡教程
郑重声明：本实验并不是对所有SD卡都能成功运行
第一步：打开winhex软件，用读卡器读SD卡，在winhex中查看SD卡
点这
点击查找（ctrl+F）
输入FAT（找到DBR处）
发现DBR起始于0x11200扇区地址，它必是512整数倍，因为一个扇区含512BYTE，所以在程序中读一个扇区时一定要是512整数倍，否则会出错。11200地址对应的值是0xEB，本程序读一下这个地址的值看看是否正确。注意有的winhex编址是十进制
看看程序吧
#include
#define uchar unsigned char
#define uint unsigned int
//=============================================================
//定义SD卡需要的4根信号线
sbit SD_CLK = P1^1;
sbit SD_DI = P1^2;
sbit SD_DO = P1^0;
sbit SD_CS = P1^3;
sbit Beep=P2^0;//用来调程序标志
//===========================================================
//===========================================================
//定义512字节缓冲区，，89C52直接定义成unsigned char DATA[80];，太大了RAM不够unsigned char xdata DATA[512];
void delay(unsigned int z)
{
unsigned int x,y;
for(x=z;x>0;x--);
for(y=110;y>0;y--);
}
//=========================================================== //写一字节到SD卡,模拟SPI总线方式
void SdWrite(unsigned char n)
{
unsigned char i;
for(i=8;i;i--)
{
SD_CLK=0;
SD_DI=(n&0x80);
n<<=1;
SD_CLK=1;
}
SD_DI=1;
}
//=========================================================== //从SD卡读一字节,模拟SPI总线方式
unsigned char SdRead()
{
unsigned char n,i;
for(i=8;i;i--)
{
SD_CLK=1;
SD_CLK=0;
n<<=1;
if(SD_DO) n|=1;
}
return n;
}
//============================================================ //检测SD卡的响应
unsigned char SdResponse()
{
uchar i=0,response=0;
while(i<=8)
{
response = SdRead();
if(response==0x00)
break;
if(response==0x01)
break;
i++;
}
return response;
}
//================================================================ //发命令到SD卡
void SdCommand(unsigned char command, unsigned long argument, unsigned char CRC) {
SdWrite(command|0x40);
/*SdWrite(((unsigned char *)&argument)[0]);
SdWrite(((unsigned char *)&argument)[1]);
SdWrite(((unsigned char *)&argument)[2]);
SdWrite(((unsigned char *)&argument)[3]);*/
SdWrite(argument>>24);
SdWrite(argument>>16);
SdWrite(argument>>8);
SdWrite(argument);
SdWrite(CRC);
}
//================================================================ //初始化SD卡
unsigned char SdInit(void)
{
unsigned char i;
unsigned char response=0xFF;
P3=0xff;
SD_CS=1;
for(i=0;i<=0xfe;i++)
SdWrite(0xff);
SD_CS=0;
SdCommand(0x00,0,0x95);
SD_DI=1;
response=SdResponse();
if(response!=0x01)
{
return 0;
}
if(response==0x01)
{ //不管什么SD卡都能进入这一步，同时也说明硬件没问题SD_CS=1;
//Beep=0;
//while(1);//用来查看程序能否运行到这一步，去掉//即可
SdWrite(0xff);
SD_CS=0;
while(1)
{
SdCommand(0x01,0,0xff);//SdCommand(0x01,0x00000000,0xff);//进SPI
response=0xff;
SD_DI=1;
for(i=0;i<250;i++)//response!=0x00//等待回复
{
response=SdResponse(); //Beep=0;/
if(response==0) break;
}
if(response==0) {break;}//回复0则通过SPI，只要通过SPI后面的指令才能继//续
// Beep=0;
}
// Beep=0;//看程序能否跳出来，挑不出来则进不了SPI
SD_CS=1;
SdWrite(0xff);
SD_CS=0;
// Beep=0;
return 1;
}
}
//================================================================
//往SD卡指定地址写数据,一次最多512字节最好不要乱写否则fat系统被改掉SD卡打不开
unsigned char SdWriteBlock(unsigned char *Block, unsigned long address,int len)
{
unsigned int count;
unsigned char dataResp;
SD_CS=0;
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<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 DA TA RESPONSE token dataResp=SdRead(); while(SdRead()==0); dataResp=dataResp&0x0f; //mask the high byte of the DATA RESPONSE token SD_CS=1; SdWrite(0xff); if(dataResp==0x0b) { return 0; } if(dataResp==0x05)return 1; return 0; } //printf("Command 0x18 (Write) was not received by the SD.\n"); 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,i; uchar response; SD_CS=0; // while(1) // { SdCommand(0x11,address,0xff); // SD_DO=1; // P0=SdResponse(); // P0=0xff; // while(1); while(response!=0xfe && i<200) {response=SdRead();P0=response;i++;} // if(i>=200) Beep=0; // P0=0xf0; // } // Beep=0; for(count=0;count<512;count++) *Block++=SdRead(); SdRead(); SdRead(); //Now read in the DA TA RESPONSE token SD_CS=1; SdWrite(0xff); return 1; } void main() { unsigned int mm; unsigned long AddTemp=0x11200;//70144;//SD卡地址第一个数据物理地址初始值70144是通过winhex查看，对于你的SD卡肯定要改 //可以用winhex查看，一定要是512整数倍mm=SdInit(); // SdReadBlock(DATA,AddTemp,1); delay(10); // Beep=0; if(DATA[0]==0xeb) Beep=0;// 看读的对不对 while(1); }