#include <reg51.h>

#define Tick   10000     // 10000 x 100us = 1s
#define T100us (256-50)  // 100us時間常數(shù)(6M)

unsigned int C100us;     // 100us記數(shù)單元
bit LEDBuf;
sbit LED = P1^0;

void T0Int() interrupt 1
{
  C100us--;
  if (C100us == 0) {
    C100us = Tick;     // 100us 記數(shù)器為0, 重置記數(shù)器
    LEDBuf = !LEDBuf;  // 取反LED
  }
  
}

void main() 
{
  TMOD = 0x02;   // 方式2, 定時器
  TH0  = T100us;
  TL0  = T100us;

  IE   = 0x82;   // EA=1, IT0 = 1

  LEDBuf = 0;
  LED    = 0;
  C100us = Tick;
  TR0  = 1;      // 開始定時

  while (1) {
    LED = LEDBuf;
  }  
}