1.采用两种定时方式，使发光二极管闪烁。

方法一：

#include<reg52.h>

sbit LED = P0^0;
sbit ADDR0 = P1^0;
sbit ADDR1 = P1^1;
sbit ADDR2 = P1^2;
sbit ADDR3 = P1^3;
sbit ENLED = P1^4;

void main()  {
    unsigned int i = 0;  
    ENLED = 0;  
ADDR3 = 1;       
ADDR2 = 1;       
ADDR1 = 1;
    ADDR0 = 0;
    while (1)
    {
        LED = 0;                  
        for (i=0; i<30000; i++);  
        LED = 1;                  
        for (i=0; i<30000; i++);  
    }
}

方法二：采用中断的方式，利用数码管显示，编写从100开始倒计时的程序（可显示高位0）。

#include <reg52.h>

sbit LED = P0^0;
sbit ADDR0 = P1^0;
sbit ADDR1 = P1^1;
sbit ADDR2 = P1^2;
sbit ADDR3 = P1^3;
sbit ENLED = P1^4;

void main()
{
    unsigned char cnt = 0;  
ENLED = 0;    
ADDR3 = 1;
    ADDR2 = 1;
    ADDR1 = 1;
    ADDR0 = 0;
    TMOD = 0x01;  
    TH0  = 0xB8;  
    TL0  = 0x00;
    TR0  = 1;     
    while (1)
    {
        if (TF0 == 1)        
        {
            TF0 = 0;         
            TH0 = 0xB8;      
            TL0 = 0x00;
            cnt++;           
            if (cnt >= 50)           
            {
                cnt = 0;     
                LED = ~LED;          
             }
         }
    }
}

2.采用中断的方式，利用数码管显示，编写从100开始倒计时的程序（可显示高位0）。

#include <reg52.h>

sbit ADDR0 = P1^0;
sbit ADDR1 = P1^1;
sbit ADDR2 = P1^2;
sbit ADDR3 = P1^3;
sbit ENLED = P1^4;

unsigned char code LedChar[] = { 
    0xC0, 0xF9, 0xA4, 0xB0, 0x99, 0x92, 0x82, 0xF8,
    0x80, 0x90, 0x88, 0x83, 0xC6, 0xA1, 0x86, 0x8E };
unsigned char LedBuff[3] = { 0xFF, 0xFF, 0xFF};
unsigned char i,j = 0;   
unsigned int cnt = 0;  
unsigned char flag1s = 0;  

void main()
{
    unsigned long sec = 101; 
    EA = 1;       //使能总中断
    ENLED = 0;    //使能U3，选择控制数码管
    ADDR3 = 1;    //因为需要动态改变ADDR0-2的值，所以不需要再初始化了
    TMOD = 0x01;  //设置T0为模式1
    TH0  = 0xFC;  //为T0赋初值0xFC67，定时1ms
    TL0  = 0x67;
    ET0  = 1;     //使能T0中断
    TR0  = 1;     //启动T0
    
    while (1)
    {
        if (flag1s == 1)  
        {
            flag1s = 0;   
            sec--;        
            LedBuff[0] = LedChar[sec%10];
            LedBuff[1] = LedChar[sec/10%10];
            LedBuff[2] = LedChar[sec/100%10];
		}
    }
}
void InterruptTimer0() interrupt 1
{
    TH0 = 0xFC;  //重新加载初值
    TL0 = 0x67;
    cnt++;       
    if (cnt >= 1000)  
    {
        cnt = 0;      
        flag1s = 1;   
    }
P0 = 0xFF;   
switch (i)
    {
        case 0: ADDR2=0; ADDR1=0; ADDR0=0; i++; P0=LedBuff[0]; break;
        case 1: ADDR2=0; ADDR1=0; ADDR0=1; i++; P0=LedBuff[1]; break;
        case 2: ADDR2=0; ADDR1=1; ADDR0=0; i=0; P0=LedBuff[2]; break;
        default: break;
    }
}