请教熟悉89C52的大侠

leon_1001

我编制了如下一段AD转换程序，可是发现当旋转AD转换电位器时，发光二极管正常变化 ，而数码管却一直显示255，请问是什么原因？ 

#include<reg52.h>
#define uchar unsigned char
#define uint unsigned int
sbit wr=P3^6;
sbit rd=P3^7;
sbit dula=P2^6;
sbit wela=P2^7;
sbit diola=P2^5;
uchar code tabledu[]={
0x3f,0x06,0x5b,0x4f,
0x66,0x6d,0x7d,0x07,
0x7f,0x6f};
uchar code tablewe[]={0xf7,0xef,0xdf};
uchar temp;
void delay(uint z)
{

uint t1,y;

for(t1=z;t1>0;t1--)

for(y=110;y>0;y--);
}
void display(uchar bai,uchar shi,uchar ge);
void start();
void main()
{

while(1)

{


start();

delay(1);

rd=0;
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delay(1);

rd=1;

delay(5);

temp=P1;


display(temp/100,temp%100/10,temp%10);

delay(1);

}

}
void start()
{

wela=1;

P0=0x7f;

wela=0;

wr=1;

wr=0;

wr=1;

}
void display(uchar bai,uchar shi,uchar ge)
{

wela=1;

P0=tablewe[0];


wela=0;



dula=1;

P0=tabledu[bai];

dula=0;

delay(1);



wela=1;

P0=tablewe[1];

wela=0;



dula=1;

P0=tabledu[shi];

dula=0;

delay(1);


wela=1;

P0=tablewe[2];


wela=0;




dula=1;

P0=tabledu[ge];

dula=0;

delay(1);
}