曼徹斯特編碼的接收C51程序

曼碼接收程序，常用在無線信號的編碼與解碼中，給大家分享：

rxi()
{
    // this routine gets called every time TMR0 overflows
    if(T0IF)  //定時器中斷程序
    {
        TMR0 = PERIOD;             // 裝計時器初值
        T0IF = 0;     // 清定時器溢出標志
        XTMR++;                     // 外部的系統時鐘計時器加1
        RFcount++;     // 脈沖寬度計數器加1
  return;
    }
    if(RAIF)  //端口電平變化中斷程序
    {
     if (RFFull)                 // 如果接收位滿就退出
         return;
  RFBit = RFIn;               // 取樣信號接收的值
  RAIF = 0;
     switch (RFstate)            // 當前狀態
     {
      case TRFDATAUP:
    switch (RFcount)
    { 
        case 4:
        case 5:  
        case 6:
        case 7:
      PORTA = PORTA;//啟動端口電平中斷
        break;
     
        case 8:
        case 9:
        case 10:
        case 11:
        case 12:
      B[Bptr] <<= 1;              // rotate 
      if ( RFBit==0)  //如是有效的下跳變則該位的數據值為1,上跳變為0
      { 
       B[Bptr]+=1;          // shift in bit
      }
      if ( ( ++BitCount & 7) == 0)
       Bptr++;                 // advance one byte 
      if (BitCount == NBIT)
      {
       RFstate = TRFreset;     // finished receiving 
       RFFull = 1;
      } 
      RFcount=0; //重新記時
      PORTA = PORTA;//啟動端口電平中斷
         break;
   
        default:  //超時或不足則退出接收
            RFstate = TRFSYNC;        // reset state machine in all other cases
            RFcount = 0;
            Bptr = 0;
            BitCount = 0;
      PORTA = PORTA;//啟動端口電平中斷
    }
   break;
   case TRFSYNC:
          if ( RFBit)
          { // rising edge detected  +---+                +---..
            //                       |   |  <-Theader->   |   
            //                           +----------------+
              if ( ( RFcount < SHORT_HEAD) || ( RFcount >= LONG_HEAD))
              {
                  RFstate = TRFreset;
      PORTA = PORTA;//啟動端口電平中斷
                  break;                  // too short/long, no header
              }
              else
              {
                  RFcount =0;             // restart counter
                  RFstate= TRFDATAUP;
      PORTA = PORTA;//啟動端口電平中斷
              }
          }
          else
          { // still low
              RFcount=0;
     PORTA = PORTA;//啟動端口電平中斷
          }
          break;

     case TRFreset:
     default:
         RFstate = TRFSYNC;        // reset state machine in all other cases
         RFcount = 0;
         Bptr = 0;
         BitCount = 0;
      PORTA = PORTA;//啟動端口電平中斷
         break;
         
     } // switch
    } //電平中斷   
} // rxi 


void InitReceiver()
{
IOCA = 2;
    T0IF = 0;
    T0IE = 1;                   // TMR0 overflow interrupt
RAIE = 1;     //使能端口電平變化中斷
    GIE = 1;                    // enable interrupts
    RFstate = TRFreset;         // reset state machine in all other cases
    RFFull = 0;                 // start with buffer empty
    XTMR = 0;                   // start extended timer
    TMR0 = PERIOD;             // 裝計時器初值
    PORTA = PORTA;//啟動端口電平中斷
}

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