单片机memoirs 11 MAX232 On May 6,2013

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#include //接收数据
unsigned char a;
unsigned char l,h,key;
void delay(unsigned t)
{
   while(t--);
}
void main()
{
  
  TMOD=0X20;
  TH1=0XFD;
  TL1=0XFD;
  TR1=1;
  SM0=0;
  SM1=1;
  REN=1;
  EA=1;
  ES=1;
  P1=0xff;
  while(1)
  {
   P2=0xf0;
  l=P2;
  l=l&0xf0;
  if(l!=0xf0)
    {
  delay(200);
  if(l!=0xf0)
    {
  l=P2&0xf0;
  l=l|0x0f;
  P2=l;
  h=P2;
  h=h&0x0f;
  l=l&0xf0;
  key=l+h;
}
}
switch(key)
   {
    case 0xee:SBUF=0xc0;break;
  case 0xde:SBUF=0xf9;break;
  case 0xbe:SBUF=0xa4;break;
  case 0x7e:SBUF=0xb0;break;
  case 0xed:SBUF=0x99;break;
  case 0xdd:SBUF=0x92;break;
  case 0xbd:SBUF=0x82;break;
  case 0x7d:SBUF=0xf8;break;
  case 0xeb:SBUF=0x80;break;
  case 0xdb:SBUF=0x90;break;
  case 0xbb:SBUF=0x88;break;
  case 0x7b:SBUF=0x83;break;
  case 0xe7:SBUF=0xc6;break;
  case 0xd7:SBUF=0xa1;break;
  case 0xb7:SBUF=0x86;break;
  case 0x77:SBUF=0x8e;break;
   }   
  }
}
void  usbchuan() interrupt 4
{
   a=SBUF;
   P1=a;
   RI=0;
}
 c: