unsigned char MMC_read_sector(unsigned int addr,unsigned char *Buffer)
{
unsigned char temp;
unsigned int i;

SPI_TransferByte(0xff);
temp = Write_Command_MMC(MMC_READ_BLOCK,addr<<9);
if(temp != 0x00)
{
  return(READ_BLOCK_ERROR);
}

while(SPI_TransferByte(0xff) != 0xfe);

for(i=0;i<512;i++)
{
  *Buffer++ = SPI_TransferByte(0xff);
}
// SPI_TransferByte(0xff);
// SPI_TransferByte(0xff);
  SPI_TransferByte(0xFF);
  SPI_TransferByte(0xFF);
return (1);
}

*Buffer++ = SPI_TransferByte(0xff);这是在读数据吗，读数据进buffer，为什么要传入0xff