以查询方式实现1s定时

#include <reg52.h>

sbit LED = P0^2;    
unsigned int vT = 0;

void main ()
{
    LED = 0;         // 点亮
    TMOD = 0x01;     // 定时模式1 16位定时计数器
    TR0 = 1;         // 启动定时器0
    TH0 = 0x3C;         // 计数初值 15536 (65536-15536=50000 * 1us = 50ms)
    TL0 = 0xB0;    
    while(1)
    {
        if (TF0 == 1)
        {
           TF0 = 0;            // 清除标志位
           vT++;
           if (vT == 20)    // 20 * 50 = 1000ms = 1s
           {
                vT = 0;
                TH0 = 0x3C;     // 计数初值 15536
                TL0 = 0xB0;    
                LED = !LED;     // 溢出后切换led状态
           }
        }
    }
}