//定义SD卡需要的4根信号线
sbit SD_CLK = P2^1;
sbit SD_DI = P2^2;
sbit SD_DO = P2^0;
sbit SD_CS = P2^3;
sbit p0 = P0^0;
sbit p1 = P0^1;
sbit p2 = P0^2;
sbit p3 = P0^3;
//===========================================================
unsigned char man=0;
//===========================================================
//定义512字节缓冲区，注意需要使用 xdata关键字
unsigned char xdata DATA[512];
void Delay(unsigned int i)
{
while(i--);
}
//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!= 0;i--)
{
SD_DI=(n&0x80);
n<<=1;
SD_CLK=0;
if(man==1)
Delay(4);
SD_CLK=1;
if(man==1)
Delay(4);
}
}
//===========================================================
//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!= 0;i--)
{
n<<=1;
SD_CLK=0;
if(SD_DO) n|=1;
if(man==1)
Delay(4);
SD_CLK=1;
if(man==1)
Delay(4);
}
return n;
}
//============================================================
//检测SD卡的响应
unsigned char SdResponse()
{
unsigned char i=0,response;
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(CRC);
}
//================================================================
//初始化SD卡
unsigned char SdInit(void)
{
unsigned char time,temp,i;
SD_CS=1;
for(i=0;i<=9;i++)
SdWrite(0xff);
SD_CS=0;
time=0;
temp=10;
man=1;
do
{
SdCommand(0x00,0,0x95);
temp=SdResponse();
time++;
if(time>200)
p3=0;//CMD0没过
}
while(temp!=0x01);
if(temp==0x01)
p0=0;//CMD0通过
time=0;
SD_CS=1;
SdWrite(0xff);
SD_CS=0;
do
{
SdCommand(0x01,0x00ffc000,0xff);
temp=SdResponse();
if(temp==0)
{p1=0;;//CMD1通过
return 0;}
time++;
}
while(time<200);
if(time>180)
p2=0;//CMD1没过
else
p2=1;
man=0;
return 0;
}
//================================================================
//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 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<len;count++) SdWrite(*Block++);
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\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;
}
//=======================================================================
//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\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<len;count++) *Block++=SdRead();
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;
}
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