单片机串口通信有问题

#include<reg51.h>
#include<math.h>
#include <string.h>
sbit p00=P0^1; //LED位选
sbit p01=P0^2;
sbit p02=P0^3;
unsigned char code displaycode[]={0xC0,0xF9,0xA4,0xB0,0x99,0x92,0x82,0xF8,0x80,0x90};
unsigned int g,s,bai;
int wendu;
//int wendu1[3];
//char w=0;

void delayMS(unsigned int i)
{
unsigned char k,j;
for(k=0;k<i;k++)
for(j=0;j<200;j++);
}

void display(){
P0=0xff&0xf7;
//p00=0;
P2=displaycode[bai];
delayMS(5);

P0=0xff&0xfb;
//p01=0;
P2=displaycode[s]; //s
delayMS(5);

P0=0xff&0xfd;
//p02=0;
P2=displaycode[g]; //g
delayMS(5);
}
void convert(unsigned long y){
bai=y/100;
s=y%100/10;
g=y%100%10;
}

void init_chuankou(void)
{
TMOD=0x20;
TH1=0xf3;
TL1=0xf3;
SCON=0x50;
PCON=0x80;
TR1=1;
ES=1;
EA=1;
}


void main()
{
init_chuankou();
while(1)
{
/* if(w==3)
{ wendu=100*wendu1[0]+10*wendu1[1]+wendu1[2];
w=0; } */
convert(wendu);
display();
}
}

void chuankou(void) interrupt 4
{
while(RI==0);
RI=0;
/* if(w==0)
{
wendu1[0]=SBUF;
w=1;
}
else if(w==1)
{
wendu1[1]=SBUF;
w=2;
}
else if(w==2)
{
wendu1[2]=SBUF;
w=3;
}
else; */
wendu=SBUF;
SBUF=wendu;
while(TI==0);
TI=0;
// convert(wendu);
// display();
// while(1);
}

本来是想做串口发送一个数在数码管上显示的，但始终显示不对，调试时，数码管显示的始终为-2且只有一位有效，请高手指点，我需要能在0~999之间的显示，