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曼彻斯特编码的接收C51程序

作者:佚名   来源:本站原创   点击数:  更新时间:2012年01月18日   【字体:
曼码接收程序,常用在无线信号的编码与解码中,给大家分享:

rxi()
{
    // this routine gets called every time TMR0 overflows
    if(T0IF)  //定时器中断程序
    {
        TMR0 = PERIOD;             // 装计时器初值
        T0IF = 0;     // 清定时器溢出标志
        XTMR++;                     // 外部的系统时钟计时器加1
        RFcount++;     // 脉冲宽度计数器加1
  return;
    }
    if(RAIF)  //端口电平变化中断程序
    {
     if (RFFull)                 // 如果接收位满就退出
         return;
  RFBit = RFIn;               // 取样信号接收的值
  RAIF = 0;
     switch (RFstate)            // 当前状态
     {
      case TRFDATAUP:
    switch (RFcount)
    { 
        case 4:
        case 5:  
        case 6:
        case 7:
      PORTA = PORTA;//启动端口电平中断
        break;
     
        case 8:
        case 9:
        case 10:
        case 11:
        case 12:
      B[Bptr] <<= 1;              // rotate 
      if ( RFBit==0)  //如是有效的下跳变则该位的数据值为1,上跳变为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; //重新记时
      PORTA = PORTA;//启动端口电平中断
         break;
   
        default:  //超时或不足则退出接收
            RFstate = TRFSYNC;        // reset state machine in all other cases
            RFcount = 0;
            Bptr = 0;
            BitCount = 0;
      PORTA = PORTA;//启动端口电平中断
    }
   break;
   case TRFSYNC:
          if ( RFBit)
          { // rising edge detected  +---+                +---..
            //                       |   |  <-Theader->   |   
            //                           +----------------+
              if ( ( RFcount < SHORT_HEAD) || ( RFcount >= LONG_HEAD))
              {
                  RFstate = TRFreset;
      PORTA = PORTA;//启动端口电平中断
                  break;                  // too short/long, no header
              }
              else
              {
                  RFcount =0;             // restart counter
                  RFstate= TRFDATAUP;
      PORTA = PORTA;//启动端口电平中断
              }
          }
          else
          { // still low
              RFcount=0;
     PORTA = PORTA;//启动端口电平中断
          }
          break;

     case TRFreset:
     default:
         RFstate = TRFSYNC;        // reset state machine in all other cases
         RFcount = 0;
         Bptr = 0;
         BitCount = 0;
      PORTA = PORTA;//启动端口电平中断
         break;
         
     } // switch
    } //电平中断   
} // rxi 


void InitReceiver()
{
IOCA = 2;
    T0IF = 0;
    T0IE = 1;                   // TMR0 overflow interrupt
RAIE = 1;     //使能端口电平变化中断
    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;             // 装计时器初值
    PORTA = PORTA;//启动端口电平中断
}
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