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SD卡接口程序，基于ATmega32，編寫ICCAVR6.31A

[code="C"]

/************************************************************/
/*           SD Code for   M32L             */
/*       By   pasyong        */
/*       2006-4         */
/*       Base ICC6.31A             */
/************************************************************/
#include <iom32v.h>
#include <macros.h>
#include "1011.h"
#define uchar unsigned char
#define uint unsigned int
#define MMC_CS_PIN     BIT(4)    //PORTB.4
#define MMC_PORT       PORTB   

 uchar reading=0,a=0,pointer=0;
void sd_port_init()
{
MMC_PORT =MMC_CS_PIN;
}
uchar BUFFER[512];                   //扇區緩沖區
uint i=0;
void delay_nus(uint n)
 {
 unsigned char  b;
  for (b = 1; b<n; b++)
   ;
 }
//****************************************************************************
//Send a Command to MMC/SD-Card
//Return: the second byte of response register of MMC/SD-Card
//****************************************************************************
uchar SD_Write_Command(uchar cmd,unsigned long arg)
{
   uchar tmp;
   uchar retry=0;
  
   //MMC_PORT =MMC_CS_PIN;       //SD卡關閉  
   //send 8 Clock Impulse
   Write_Byte_SPI(0xFF);
  
   //set MMC_Chip_Select to low (MMC/SD-Card active)
  MMC_PORT&=~MMC_CS_PIN;       //SD卡使能

   Write_Byte_SPI(cmd 0x40);   //送頭命令
   Write_Byte_SPI(arg>>24);
   Write_Byte_SPI(arg>>16);     //send 6 Byte Command to MMC/SD-Card
   Write_Byte_SPI(arg>>8);
   Write_Byte_SPI(arg&0xff);
   Write_Byte_SPI(0x95);       //僅僅對RESET有效的CRC效驗碼
 
   //get 8 bit response
   //Read_Byte_MMC(); //read the first byte,ignore it.
   do
   {  //Only last 8 bit is used here.Read it out.
      tmp = Read_Byte_SPI();
      retry++;
   }
   while((tmp==0xff)&&(retry<100));  //當沒有收到有效的命令的時候
  
   if(reading==0)
   MMC_PORT =MMC_CS_PIN;            //MMC_CS_PIN=1;
   else MMC_PORT&=~MMC_CS_PIN;      //MMC_CS_PIN=0;  
   return(tmp);
}
//****************************************************************************
//SD卡初始化(SPI-MODE)
//****************************************************************************
uchar SD_Init(void)
{ 
   uchar retry,temp;
   uchar i;
   MMC_PORT&=~MMC_CS_PIN;      //SD卡使能
 
  delay_nus(250);  //Wait MMC/SD ready...
   for (i=0;i<0x0f;i++)
   {
      Write_Byte_SPI(0xff); //send 74 clock at least!!!
   }
   //Send Command CMD0 to MMC/SD Card
   retry=0;
  
   do
   { //retry 200 times to send CMD0 command
     temp=SD_Write_Command(0,0);
     retry++;
     if(retry==100)
     {
      ;//CMD0 Error!
     }
   }
   while(temp!=1); 
  
   //Send Command CMD1 to MMC/SD-Card
   retry=0;
   do
   { //retry 100 times to send CMD1 command
     temp=SD_Write_Command(1,0);
     retry++;
     if(retry==100)
     {
     ;
     }
   }
   while(temp!=0);
   retry=0;
    SD_Write_Command(16,512);     //設置一次讀寫BLOCK的長度為512個字節
 
   MMC_PORT =MMC_CS_PIN;   //MMC_CS_PIN=1;  //set MMC_Chip_Select to high
   return(0); //All commands have been taken.
}
//****************************************************************************
//從SD卡讀一個扇區  Return 0 if no Error.
//****************************************************************************
uchar SD_Read_Block(unsigned long address)
{ 
   uchar temp=0;uint i=0;
   reading=1;
   temp=SD_Write_Command(17,address);     //讀出RESPONSE    
   while (Read_Byte_SPI()!= 0xfe)
   {;}  //直到讀取到了數據的開始頭0XFE,才繼續
   for(i=0; i<512; i++)
 {
 BUFFER[i]=Read_Byte_SPI();
 }
   Read_Byte_SPI();//CRC - Byte
   Read_Byte_SPI();//CRC - Byte
   reading=0;
   MMC_PORT =MMC_CS_PIN;        //關閉SD卡
   return(temp);
}

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