数字电压表程序

#include<reg52.h>//
#define uchar unsigned char
sbit sda=P2^7; //数据线
sbit scl=P2^6; //信号控制线
sbit key1=P1^3;
sbit relay=P1^1;
uchar a;
bit wl;
uchar led_discode[11]={0xc0,0xf9,0xa4,0xb0,0x99,
                       0x92,0x82,0xf8,0x80,0x90,0xff}; 
void delay()
{ ;; }
void start()  //开始信号
{   
    sda=1;
    delay();
    scl=1;
    delay();
    sda=0;
    delay();
}

void stop()   //停止
{
    sda=0;
    delay();
    scl=1;
    delay();
    sda=1;
    delay();

}

void respons()  //应答
{
    uchar i;
    scl=1;
    delay();
    while((sda==1)&&(i<250))i++;
    scl=0;
    delay();
}

void init()    //函数初始化
{
    sda=1;
    delay();
    scl=1;
    delay();
}

void write_byte(uchar date)//写地址选择某个硬件，或者选择硬件内寄存地址
{
    uchar i,temp;
    temp=date;


    for(i=0;i<8;i++)
    {
        temp=temp<<1;
        scl=0;