在看SD卡实验（SPI）遇到不明白的（已解决）

bluesky_kun · 发表于 2011-3-31 16:49:01

u8 SD_WaitDataReady(void)
{
    u8 r1=MSD_DATA_OTHER_ERROR;
    u32 retry;
    retry=0;
    do
    {
        r1=SPIx_ReadWriteByte(0xFF)&0X1F;//????????
        if(retry==0xfffe)return 1;
  retry++;
  switch (r1)
  {
   case MSD_DATA_OK://???????????·??
    r1=MSD_DATA_OK;
    break;
   case MSD_DATA_CRC_ERROR: //CRC???é?í?ó
    return MSD_DATA_CRC_ERROR;
   case MSD_DATA_WRITE_ERROR://?????????í?ó
    return MSD_DATA_WRITE_ERROR;
   default://?????í?ó
    r1=MSD_DATA_OTHER_ERROR;
    break;
  }
    }while(r1==MSD_DATA_OTHER_ERROR); //?????í?ó?±???±????
retry=0;
while(SPIx_ReadWriteByte(0XFF)==0)//??????????0,?ò???????????ê??
{
  retry++;
  //delay_us(10);//SD?¨???????è?????¤???±??
  if(retry>=0XFFFFFFFE)return 0XFF;//?????§°???
};
    return 0;//??????
} }

上面程序中红色标注的为什么要&0X1F
为什么啊？