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实验26
SD 卡SPI模式实验
SD卡全称为
Secrue Digital Memory Card，具有轻巧、可加密、传输速度高、适用于手持设备等优点。
SD需要高速读写，同时也要使手持等嵌入式设备能方便使用，特设有两个访问接口：SD模式接口和SPI接口。单片机由于速度问题一般用SPI接口（注意本机SD卡为选购件，或自行到电脑城购买
SD卡命令共分为12类，分别为class0到class11，支持命令集
如下:
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Class0 :(卡的识别、初始化等基本命令集)
CMD0:复位SD 卡.
CMD1:读OCR寄存器.
CMD9:读CSD寄存器.
CMD10:读CID寄存器.
CMD12:停止读多块时的数据传输
CMD13:读 Card_Status 寄存器
Class2 (读卡命令集):
CMD16:设置块的长度
CMD17:读单块.
CMD18:读多块,直至主机发送CMD12为止
.
Class4(写卡命令集) :
CMD24:写单块.
CMD25:写多块.
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CMD27:写CSD寄存器 .
Class5 (擦除卡命令集):
CMD32:设置擦除块的起始地址.
CMD33:设置擦除块的终止地址.
CMD38: 擦除所选择的块.
Class6(写保护命令集):
CMD28:设置写保护块的地址.
CMD29:擦除写保护块的地址.
CMD30: Ask the card for the status of the write protection bits
class7：卡的锁定，解锁功能命令集
class8：申请特定命令集 。
class10 －11 ：保留
其中 class1,
class3,class9：SPI模式不支持
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SD卡部分的程序请看配套的光盘编程实例程序
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SD引脚
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SD模式
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SPI模式
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1
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DAT3
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CS
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2
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CMD
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DI
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3
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VSS
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VSS
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4
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VDD
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VDD
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5
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CLK
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SCLK
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6
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VSS
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VSS
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7
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DAT0
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DO
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8
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DAT1
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Resvered
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9
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DAT2
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Resvered
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1 用一根4PIN排线一端插入P1.0-1.3,另一端插入sd卡
的接口jp74.2 用两根1 pin线连接SD卡的电源到开发板的电源5V和GND3用一条8PIN的数据排线把CPU部份的P0口
（JP51）连接到八路指示灯部份的JP32烧写配套的光盘编程实例的SD卡程序， 8路跑灯开始做加1显示，如果此
时拔下SD卡，则8路跑灯停止 |
#include "HAL.H"
//============================================================
//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=0;
SD_CLK=1;
n<<=1;
if(SD_DO) n|=1;
}
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)
{
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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