51串口通信

#include <reg52.h>
unsigned char  m;  
unsigned char  flag;
unsigned char   tvb;
unsigned char   xianshi;

void main()
{
    TMOD=0x20; //设置定时器1为方式2
    TH1=0xfd;   //装入处初值
    TL1=0xfd;
    TR1=1; //启动定时器
    SM0=0;// 
    SM1=1;  //  shezhifangshi1
    REN=1;//接收使能
    EA=1;
    ES=1;
    while(1)
    {
           if(tvb==1) 
        {
            ES=0;
            tvb=0;
            SBUF=m;
            while(!TI);//等待数据发送结束
            TI=0;
            ES=1;
        }
    }
}
void chuakou()  interrupt 4
{
    m = SBUF;
    if(m > 0 && m <= 6)
        flag = 1;
    else if( m >= 7 && m <= 13)
        flag = 2;
    else if( m >= 14 && m <= 20)
        flag = 3;
    else
        flag = 0xff;

    switch( flag )
    {
        case 1: 
            P1 = 0xfe;
            break;
        case 2: 
            P1 = 0xfd;
            break;
        case 3: 
            P1 = 0xfb;
            break;
        case 0xff:
            P1 = 0xff;
            break;
        default:
            P1 = 0xff;
            break;
    } 
    RI = 0;
    tvb = 1;//标志
}