// 12MHz晶振
#include "reg52.h"
#include "intrins.h"

#define time (65536-50000) // 单次定时50ms
unsigned char cn;
unsigned char temp;

void main(void)
{
      cn=10; //10*50ms=0.5s
      temp=0x7f;

    TMOD = 0x10;                    //set timer1 as mode1 (16-bit)
    TL1 = time;                     //initial timer1 low byte
    TH1 = time >> 8;                //initial timer1 high byte
    TR1 = 1;                        //timer1 start running
    ET1 = 1;                        //enable timer1 interrupt
      IT0 = 1;                        //set INT0 int type (1:Falling 0:Low level)
    EA = 1;                         //open global interrupt switch
    
      while(1);

}

/* Timer0 interrupt routine */
void tm1_isr() interrupt 3
{
    TL1 = time;                    
    TH1 = time >> 8;               
    if (cn-- == 0)               
    {
        cn = 10;  
              P1=temp;
        temp=_cror_(temp,1);    
    
    }
}