问个12c5a60s2的内部ADC问题

我开机后显示电压为2.44，ADC引脚接地显示0。怎么回事啊程序在下面：
#include <STC12C5A60S2.H>
#define uchar unsigned char
#define uint unsigned int
uchar t1num,x;
uchar code table[]=
{0xc0,0xf9,0xa4,0xb0,
0x99,0x92,0x82,0xf8,
0x80,0x90};
void delayms(uint x)
{
uint i;uchar j;
for(i=x;i>0;i--)
for(j=110;j>0;j--);
}
void AD_init()
{
P1M0=0x01;
P1M1=0x01;
ADC_CONTR=0XE0;
delayms(1000);
}
int get_AD(uchar channel)
{
uchar AD_finished=0;
int result;
ADC_CONTR|=channel;
ADC_CONTR|=0x08;
while(AD_finished==0)
{
AD_finished=(ADC_CONTR&0x10);
}
result=ADC_RES*4+ADC_RESL;
ADC_CONTR&=0xe7;
return (result);
}
float AD_AV(uchar channel)
{
float val_AV=0;
uchar num;
for(num=100;num>0;num--) //取100次的平均值
{
val_AV+=get_AD(channel);
}
val_AV/=100.0;
val_AV=(val_AV*5.0/1024)*100+0.5;
return(val_AV);
}
void main()
{
uchar x1,x2,x3;
CLK_DIV=0x01;
AD_init();
while(1)
{
x=AD_AV(7);
x1=x/100;
x2=x/10%10;
x3=x%10;
P2=0x80;
P0=table[x1]-0x80;//显示出点
delayms(50);
P0=0xff;
P2=0x40;
P0=table[x2];
delayms(50);
P0=0xff;
P2=0x20;
P0=table[x3];
delayms(50);
P0=0xff;
}
}