SD卡，是一種基于半導體快閃記憶器的新一代記憶設備，SD于1999年8月研制成功，其重量只有2克。但卻擁有高記憶容量、快速數(shù)據傳輸率、極大的移動靈活性以及很好的安全性。SD卡也很容易重新格式化，有廣泛的應用領域，如音樂、電影、新聞等多媒體文件都可以方便地保存，數(shù)碼相機也開始支持SD卡。SD卡容量最高能達到4GB。

SD卡在24mm×32mm×2.1mm的體積內結合了〔SanDisk〕快閃記憶卡控制與MLC（Multilevel Cell）技術和Toshiba（東芝）0.16u及0.13u的NAND技術，通過9針的接口界面與專門的驅動器相連接，不需要額外的電源來保持其上記憶的信息。而且它是一體化固體介質，沒有任何移動部分，所以不用擔心機械運動的損壞。

SD卡(Secure Digital Memory Card)是一種基于半導體閃存工藝的存儲卡，1999年，由日本松下、東芝及美國SanDisk公司共同研制完成。2000年，這幾家公司發(fā)起成立了SD協(xié)會(Secure Digital Association簡稱SDA)，陣容強大，吸引了大量廠商參加。其中包括IBM，Microsoft，Motorola，NEC、Samsung等。在這些領導廠商的推動下，SD卡已成為目前消費數(shù)碼設備中應用最廣泛的一種存儲卡。SD卡具有大容量、高性能、安全等多種特點的多功能存儲卡，它比MMC卡多了一個進行數(shù)據著作權保護的暗號認證功能(SDMI規(guī)格)，讀寫速度比MMC卡要快4倍。

好了，既然這么好，我們在這里給出51單片機讀寫2G SD卡程序:

#include //程序通過調試
#include
//===================================
//定義SD卡需要的4根信號線
sbit SD_CLK = P3^7;
sbit SD_DI = P3^5;
sbit SD_DO = P3^6;
sbit SD_CS = P3^4;
//========================================
//定義按鍵端口
sbit KEY = P2^7;
//========================================
//定義512字節(jié)緩沖區(qū)，注意需要使用 xdata關鍵字
unsigned char xdata DATA[512];

void delayms(unsigned int count)
{
int i,j;
for(i=0;i
{
for(j=0;j<260;j++);
}
}
//=======================================
//寫一字節(jié)到SD卡,模擬SPI總線方式
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;
}
//===========================================================
//從SD卡讀一字節(jié),模擬SPI總線方式
unsigned char SdRead()
{
unsigned char n,i;
for(i=8;i;i--)
{
SD_CLK=0;
SD_CLK=1;
n<<=1;
if(SD_DO) n|=1;

}
return n;
}
//============================================================
//檢測SD卡的響應
unsigned char SdResponse()
{
unsigned char i=0,response;

while(i<=8)
{
response = SdRead();
if(response==0x00)
break;
if(response==0x01)
break;
i++;
}
return response;
}
//=========================================================
//發(fā)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(CRC);
}
//=========================================================
//初始化SD卡
unsigned char SdInit(void)
{
int delay=0, trials=0;
unsigned char i;
unsigned char response=0x01;

SD_CS=1;
for(i=0;i<=9;i++)
SdWrite(0xff);
SD_CS=0;

//Send Command 0 to put MMC in SPI mode
SdCommand(0x00,0,0x95);

response=SdResponse();

if(response!=0x01)
{
return 0;
}

while(response==0x01)
{
SD_CS=1;
SdWrite(0xff);
SD_CS=0;
SdCommand(0x01,0x00ffc000,0xff);
response=SdResponse();
}

SD_CS=1;
SdWrite(0xff);
return 1;
}
//================================================================
//往SD卡指定地址寫數(shù)據,一次最多512字節(jié)
//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); //兩字節(jié)CRC校驗, 為0XFFFF 表示不考慮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\n");
return 0;
}
if(dataResp==0x05)
return 1;

//printf("Invalid data Response token.\n");
return 0;
}
//printf("Command 0x18 (Write) was not received by the MMC.\n");
return 0;
}

//從SD卡指定地址讀取數(shù)據,一次最多512字節(jié)
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\n");

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.\n");
return 0;
}
void initbaud(void)
{
TMOD=0X20;
TH1=0XFD;
TL1=0XFD;
PCON=0X00;
TR1=1;
SCON=0X50;//8位波特可變
//SCON=0X52;//8位波特可變 TI開中斷
}
//=================================
//主程序
main()
{
unsigned int i;
unsigned long AddTemp=331264;//SD卡地址第一個數(shù)據物理地址初始值，可以用winhex查看，這里是641物理扇區(qū)，512x641=328192，根據實際SD卡內容更改
delayms(5);
SdInit(); //SD卡初始化
while(1)
{
SdWriteBlock(AddTemp,512);
delayms(1000);
AddTemp=331264;
SdReadBlock(DATA,AddTemp,512);//每次讀出512字節(jié)放到緩沖區(qū)
initbaud();
for(i=0;i<512;i++)
{
SBUF=DATA[i];
while(!TI);
TI=0;
delayms(1);
}
while(KEY); //等待按鍵按下繼續(xù)執(zhí)行
}
}
可以在串口中看到SD卡中被寫入的數(shù)據