stc12 MCU LED_PWM dimming

This program has 3 files listed below:

stc12c5a.h Header file download: http://www.51hei.com/mcu/3282.html

main.c
 #include "stc12c5a.h"
#include "type.h"

#define FRE 22118400
#define TIME_FRE 10000 //Time 1/10000=0.0001s=0.1ms (This time is used to speed up the LED flashing frequency)
#define T0RELOAD (65536 - (FRE / TIME_FRE))

//***************************************Initialize variables
volatile U32 SYS_TIME = 0;
volatile U32 LED_PWM = 0;

//*****************************************延时函数
void delay(U32 dly)
{
    U32 i;
    while(--dly > 0)
    {
        for(i=0;i++;i<1000000);
    }
}[page]

//********************************************Timer0 initialization function
void Timer0_Init()
{
 TMOD &= 0XF0;
 TMOD |= 0X01; //16-bit counting mode of timer 0
 
 TH0 = T0RELOAD / 256;
 TL0 = T0RELOAD % 256;
 AUXR |= 0X80; //Counter 0 clock is Fosc, that is, 1T
 PT0 = 1; //Timer 0 priority control bit, 1 is high priority 0 is low priority
 EA = 1; //Open total interrupt
 ET0 = 1; //Open timer 0 interrupt
 TR0 = 1; //Start timer 0
}

//********************************************Main function
void main()
{
 Timer0_Init();
 //Modify the program according to actual situation
 while(1)
 {
  P33 = 1;
  if(P33 == 0) // KEY1
  {
   delay(5000);
   if(P33 == 0)
   {
    LED_PWM = 0; // Turn off LED
   }
  }
  
  P34 = 1;
  if(P34 == 0) // KEY2 button is kept pressed, KED gradually becomes brighter
  {
   delay(5000);
   if(P34 == 0)
   {
    if(LED_PWM < 100)
    LED_PWM ++;
   }
  }
  
  P35 = 1;
  if(P35 == 0) // KEY3 button is kept pressed, KED gradually becomes darker
  {
   delay(5000);
   if(P35 == 0)
   {
    if(LED_PWM >0)
    LED_PWM --;
   }
  }
 }
 

}
//*********************************************Timer0 interrupt
void Timer0_Routine() interrupt 1
{
 TH0 = T0RELOAD / 256;
 TL0 = T0RELOAD % 256;
 //The following program should be modified according to the actual situation
 SYS_TIME ++;
 if(SYS_TIME < LED_PWM)
 {
  P0 = 0; //Turn on the LED
 }
 else
 {
  P0 = 0XFF; //Turn off the LED
 }
  
 if(SYS_TIME > 100)
 {SYS_TIME = 0;}

}

type.h 
 #ifndef     _TYPE_H_
#define     _TYPE_H_

 
typedef unsigned char   U8;
typedef signed   char   S8;
typedef unsigned int    U16;
typedef signed   int    S16;
typedef unsigned long   U32;
typedef signed   long   S32;

 
#endif