#include <reg52.h>
 
  sbit   BT_SND   =P1^5;   
  sbit   BT_REC   =P1^6;   
  /**********************************************   
    
  IO   口模擬232通訊程序   
    
  晶振11.0592 占用定時器0     
    
  **********************************************/   
    
  #define   MODE_QUICK   
    
  #define   F_TM   F0   
    
  #define   TIMER0_ENABLE     TL0=TH0;   TR0=1;   
  #define   TIMER0_DISABLE   TR0=0;   
    
  sbit   ACC0=       ACC^0;   
  sbit   ACC1=       ACC^1;   
  sbit   ACC2=       ACC^2;   
  sbit   ACC3=       ACC^3;   
  sbit   ACC4=       ACC^4;   
  sbit   ACC5=       ACC^5;   
  sbit   ACC6=       ACC^6;   
  sbit   ACC7=       ACC^7;   
    
  void   IntTimer0()   interrupt   1   
  {   
  F_TM=1;   
  }   
  //發送一個字符   
  void   PSendChar(unsigned   char   inch)   
  {   
  #ifdef   MODE_QUICK     
  ACC=inch;   
    
  F_TM=0;   
  BT_SND=0;   //start   bit     
  TIMER0_ENABLE;   //啟動   
  while(!F_TM);   
    
  BT_SND=ACC0;   //先送出低位   
  F_TM=0;   
  while(!F_TM);   
    
  BT_SND=ACC1;     
  F_TM=0;   
  while(!F_TM);   
    
  BT_SND=ACC2;     
  F_TM=0;   
  while(!F_TM);   
    
  BT_SND=ACC3;     
  F_TM=0;   
  while(!F_TM);   
    
  BT_SND=ACC4;     
  F_TM=0;   
  while(!F_TM);   
    
  BT_SND=ACC5;     
  F_TM=0;   
  while(!F_TM);   
    
  BT_SND=ACC6;     
  F_TM=0;   
  while(!F_TM);   
    
  BT_SND=ACC7;     
  F_TM=0;   
  while(!F_TM);   
    
  BT_SND=1;     
  F_TM=0;   
  while(!F_TM);   
    
    
  TIMER0_DISABLE;   //停止timer   
  #else   
  unsigned   char   ii;   
    
  ii=0;   
    
  F_TM=0;   
  BT_SND=0;   //start   bit     
  TIMER0_ENABLE;   //啟動   
  while(!F_TM);   
    
  while(ii<8)   
  {   
  if(inch&1)   
  {   
  BT_SND=1;   
  }   
  else   
  {   
  BT_SND=0;   
  }   
  F_TM=0;   
  while(!F_TM);   
  ii++;   
  inch>>=1;   
  }   
  BT_SND=1;     
  F_TM=0;   
  while(!F_TM);   
    
  #endif     
  TIMER0_DISABLE;   //停止timer   
  }   
  //接收一個字符   
  unsigned   char   PGetChar()   
  {   
  #ifdef   MODE_QUICK     
    
  TIMER0_ENABLE;     
  F_TM=0;   
  while(!F_TM);   //等過起始位   
  ACC0=BT_REC;   
    
  TL0=TH0;   
    
  F_TM=0;   
  while(!F_TM);   
  ACC1=BT_REC;   
    
  F_TM=0;   
  while(!F_TM);   
  ACC2=BT_REC;   
    
  F_TM=0;   
  while(!F_TM);   
  ACC3=BT_REC;   
    
  F_TM=0;   
  while(!F_TM);   
  ACC4=BT_REC;   
    
  F_TM=0;   
  while(!F_TM);   
  ACC5=BT_REC;   
    
  F_TM=0;   
  while(!F_TM);   
  ACC6=BT_REC;   
    
  F_TM=0;   
  while(!F_TM);   
  ACC7=BT_REC;   
    
  F_TM=0;   
    
  while(!F_TM)   
  {   
  if(BT_REC)   
  {   
  break;   
  }     
  }   
  TIMER0_DISABLE;   //停止timer   
  return   ACC;   
  #else   
  unsigned   char   rch,ii;   
  TIMER0_ENABLE;     
  F_TM=0;   
  ii=0;   
  rch=0;   
  while(!F_TM);   //等過起始位   
    
  while(ii<8)   
  {   
  rch>>=1;   
  if(BT_REC)   
  {   
  rch|=0x80;   
  }   
  ii++;   
  F_TM=0;   
  while(!F_TM);   
    
  }   
  F_TM=0;   
  while(!F_TM)   
  {   
  if(BT_REC)   
  {   
  break;   
  }   
    
  }   
  TIMER0_DISABLE;   //停止timer   
  return   rch;   
    
  #endif     
    
  }   
  //檢查是不是有起始位   
  bit   StartBitOn()   
  {   
  return     (BT_REC==0);   
    
  }   

  void  Simulate_Com_init()
  {
   TMOD=0x02;   /*定時器1為工作模式2(8位自動重裝)，0為模式2(8位   
  自動重裝)   */   
  PCON=00;   
    
  TR0=0;   //在發送或接收才開始使用   
  TF0=0;     
  TH0=(256-96);	//9600bps   就是   1000000/9600=104.167微秒   
		//執行的  timer是   
  		//  104.167*11.0592/12=   96     
  TL0=TH0;   
  ET0=1;   
  EA=1;   
  }
  void   main()   
  {   
  unsigned   char   gch;   
    
  Simulate_Com_init();
    
  PSendChar(0x55);   
  PSendChar(0xaa);   
  PSendChar(0x00);   
  PSendChar(0xff);   
    
  while(1)   
  {   
    PSendChar(0x55);   
  if(StartBitOn())   
  {   
  gch=PGetChar();   
  PSendChar(gch);   
  }   
  }   
    
  }