51单片机信号接收问题。。。高手帮看下~~~~

 #include <c8051f020.h>
#include <intrins.h>

#define uint unsigned int
#define uchar unsigned char
sbit SPEAKER=P3^3;
sbit SLEEP=P3^1;
sbit WX_RST=P3^2;
unsigned char warning_flag;
unsigned char chaomx_flag;
unsigned char flag;
unsigned char k;
unsigned int idata c_timer0;            //计时器
unsigned char data I2C_RAM[16];        //I2C数据交换RAM
unsigned char data bat_count;      //电池采样计数
unsigned char code *pointer;
unsigned char idata uart0_se;            //uart0口接收开始同步字和结束符个数
unsigned char idata uart0_num;            //uart0口接收、发送字符个数
unsigned char idata battery_volt;        //电池电压 battery_volt=60*(battery_ad÷battery_base)
unsigned char idata battery_base[3];    //电池标称ad值和标称时的电压
unsigned int idata battery_ad;            //电池当前ad值
unsigned int idata battery_sampling[4]; //电池采样周期瞬时值

void main(void)
{
//*************************************************************
//******系统初始化*********************************************
 /*初始化------------------------------*/ 
     P1MDIN=0xFF;
    EMI0CF=0x03;
    XBR0=0x04; //00000100B       /* UART0*/
//    XBR1=0x04; //00000100B       /* INT0 */
    XBR2=0x42; //01000010B       /* 弱上拉允许，允许交叉开关，UART1不连到端口 */
//UART0初始化
    TL1=0xfd;            
    TH1=0xfd;            //定时器T1装载值  FDH(9600), FAH(4800), F4H(2400), E8(1200)
    SCON0=0x50;          //设串口UART0为模式1(用于无线通信或PC通信)  (用T1)
    SCON1=0x50;
    //定时器设定
    CKCON=0x00;          //T0,T1,T2,T4使用SYSCLK的12分频
    T2CON=0x04;           //T1为UART0串口波特率发生器，启动T2
    TMOD=0x21;            //T0为定时方式1,T1为8位自动装载为UART0串口波特率发生器
    TR1=1;                //启动T1
//DAC0设置
    
    P0MDOUT=0x01; //00000001B     /*P0配置*/
    P1MDOUT=0xff;                 /*P1*/
    P2MDOUT=0xff;                 /*P2*/
    P3MDOUT = 0xff; //11111111B  P3口配置 /*各个端口输入时配置为漏极开路，输出时配置为推挽方式*/ 
    P74OUT=0x00;
    P4=P4&0xd3;                   /*ALE=0,A16=0(P4.3),LCDE=0(P4.2)*/               
    WDTCN=0xde;                   /*暂时禁止看门狗定时器*/
    WDTCN=0xad;
    SCON1=SCON1&0xfc;    //清TI1，RI1 

//外部中断设置
    
    IE0=0;  /* 清中断标志 */
    ES0=1;            //开放串口UART0中断
    EA=1;         //开总中断
    AMX0SL=0x07;
//初始化

        P5=P5&0xfd;        //开机点亮工作灯
         while (1);


}
void uart0_rt(void) interrupt 4 
 {
           k=0;
        if( _testbit_(RI0)) 
        {
        k=SBUF0;
        }
        
 }