为什么只出现255
这个A/D 转换,将实际电压表示为二进制数#include<reg52.h>
#include<intrins.h>
#include<stdio.h>
#define uchar unsigned char
#define uint unsigned int
sbit dula=P2^6;
sbit wela=P2^7;
sbit adwr=P3^6;
sbit adrd=P3^7;
uchar flag,a;
unsigned char flag_uart,flag_time,flag_on,a,i,t0_num,ad_val;
float ad_v0;
uchar code table[]={
0x3f,0x06,0x5b,0x4f,
0x66,0x6d,0x7d,0x07,
0x7f,0x6f,0x77,0x7c,
0x39,0x5e,0x79,0x71};
void delayms(uint xms)
{
uint i,j;
for(i=xms;i>0;i--)
for(j=110;j>0;j--);
}
void init()
{
TMOD=0x21;
//SCON=0X50;
TH0=(65536-50000);
TL0=(65536-50000);
TH1=0xfd;
TL1=0xfd;
TR1=1;
ET0=1;
SM0=0;
SM1=1;
REN=1;
EA=1;
ES=1;
}
void display(uchar value)
{
uchar bai,shi,ge;
bai=value/100;
shi=value%100/10;
ge=value%10;
dula=1;
P0=table[bai];
dula=0;
P0=0xff;
wela=1;
P0=0x7e;
wela=0;
delayms(5);
dula=1;
P0=table[shi];
dula=0;
P0=0xff;
wela=1;
P0=0x7d;
wela=0;
delayms(5);
dula=1;
P0=table[ge];
dula=0;
P0=0xff;
wela=1;
P0=0x7b;
wela=0;
delayms(5);
}
uchar get_ad()
{
uchar adval;
adwr=1;
_nop_();
adwr=0;
_nop_();
adwr=1;
P1=0xff;
adwr=1;
_nop_();
adwr=0;
_nop_();
adval=P1;
adwr=1;
return adval;
}
void main()
{
init();
wela=1;
P0=0x7f;
wela=0;
while(1)
{
if(flag_uart==1)
{
flag_uart=0;
ES=0;
TI=1;
switch(flag_on)
{
case 0: puts("Turn on ad!\n");
TR0=1;
break;
case 1: printf("Turn off ad!\n");
TR0=0;
break;
case 2: puts("Error!\n");
break;
}
while(!TI);
TI=0;
ES=1;
}
if(flag_time==1)
{
flag_time=0;
ad_val=get_ad();
ad_v0=(float)ad_val*5.0/256.0;
ES=0;
TI=1;
printf("The voltage is %fV\n",ad_v0);
while(!TI);
TI=0;
ES=1;
}
display(ad_val);
}
}
void timer0() interrupt 1
{
TH0=(65536-50000);
TL0=(65536-50000);
t0_num++;
if(t0_num==20)
{
t0_num=0;
flag_time=1;
}
}
void ser() interrupt 4
{
RI=0;
a=SBUF;
flag_uart=1;
if(a==1)
flag_on=0;
else if(a==2)
flag_on=1;
else
flag_on=2;
}
但是最后只出现255,
求大神解答
