Clock program based on microcontroller timer interrupt

As long as you change the port yourself, you can use it, and the time is still relatively accurate.

#include
#define uchar unsigned char
#define uint  unsigned int

sbit RING1=P3^7; //P3^7 connects to buzzer                                       
sbit OPEN=P3^1; //LED lights up when alarm is on                    
uchar idata buffer[8]={0,0,0,0,0,0,10,11}; //define two buffers, buffer is used to temporarily store and initialize the BCD code of the time during the process
                                           

uchar code LED[]={0X3F,0X06,0X5B,0X4F,0X66,0X6D,0X7D,0X07,0X7F,0X6F,0X40,0X40}; //LED segment translation is stored in the program storage area
uchar miao=0;fen=58;shi=10; //define global variables for miao,fen,shi for storing process time
uchar _20ms; //define the global variable _20ms to count the number of interrupts, 50 for 1 second
uchar hour2,minutes2,second2; //Alarm setting time storage area
uchar hour1,minutes1,second1; //temporary storage area when modifying time
bit hour,minutes,second; //Modify the corresponding bit flag

bit add,dec; //addition and subtraction bit flags
bit openring, cancelring; //Alarm on, off, cancel flag                                            
bit setring,settime; //Alarm setting, time setting flag                                    
bit ok; // confirm the variable


 void delay_1ms(uchar x) //delay 1ms
{
  flying j;
  while(x--)
    {
      for(j=0;j<123;j++){;}
    }
}
 
 void inital(void) //Timer initialization function
{ RING1=1; //Here, when RING is equal to 0, the buzzer sounds;
   TMOD=0x01; //Timer 0 works in mode 1, using 12M crystal oscillator, timing 20ms
   TH0=(65536-20000)/256;
   TL0=(65536-20000)%256; 
   TR0=1; //TR0=1 starts the timer
   EA=1; //Open the general interrupt
   ET0=1; //Open timer interrupt
}


void timer0 (void) interrupt 1 using 1 //Timer 0 interrupt function
{ TH0=(65536-20000)/256;
   TL0=(65536-20000)%256;
    _20ms++;
    if(50==_20ms) //Judge whether it is one second
       { miao++; // one second has passed, seconds++
         _20ms=0; 

         if(miao==60) //Have you reached sixty seconds?
            { fen++; //It's time++
              miao=0;
          
              if(fen==60) //Has it reached 60 minutes?
                 { shi++; //When the time comes++
                   fen=0;
  
                 if(shi==24) //Has 24 hours arrived?
                     { shi=0; // clear to zero
                       fen=0;
                      miao=0;
                     }
                  }
              }
          }
  if(openring==1) //Is the alarm on?
    { if((shi==hour2)&&(fen==minutes2)&&(miao==second2)) //The alarm goes off when the set time comes
         RING1=0;
    if(cancelring==1) //Alarm off
            {RING1=1;cancelring=0;}
 }  
}

void timebcd (uchar m,uchar f,uchar s) //Time change function, when the timing reaches 1 second, the time will be changed             
{ 
 buffer[0]=m%10; //shi, fen, miao are converted into BCD codes, mainly for the display of digital tubes
 buffer[1]=m/10;
 buffer[2]=f%10;
 buffer[3]=f/10;
 buffer[4]=s%10;
 buffer[5]=s/10;
}


void keyscan(void) //Key scan and determine key value function, this part is the core of various clock functions
{
  uchar scode,recode,value; //Define row and column variables
  P2=0XF0; // Note the connection between keyboard and P2, 4*4 keyboard
  if ((P2 & 0XF0)!=0XF0)
     { 
      delay_1ms(10);
      if ((P2&0XF0)!=0XF0)
         {
           scode=0xfe;
     while((scode & 0x10)!=0)
              {  P2=scode;
                 if ((P2&0XF0)!=0XF0)
                   {recode=(P2 & 0XF0)|0X0f;
                      value=((~scode)+(~recode));
       switch(value)
       { case 0x11: hour=1;minutes=0;second=0;break;//, the key pressed is the function key for modification, and hour is the flag for modification
         case 0x21: hour=0;minutes=1;second=0;break;//Minutes, the key pressed is the function key for modifying minutes, and minutes is the flag for modifying minutes;
         case 0x41: hour=0;minutes=0;second=1;break;//Seconds are similar to above;
         case 0x81: add=1;dec=0;break;// 加   
         case 0x12: dec=1;add=0;break;//减
         case 0x22: setring=1;settime=0;second1=second2;minutes1=minutes2;hour1= hour2;break;//Alarm setting,
         case 0x42: settime=1;setring=0;second1=miao;minutes1=fen;hour1=shi;break;//time setting
         case 0x82: setring=0;settime=0;break;//return
         case 0x14: ok=1;break;//OK
         case 0x24: openring=1;OPEN=0;break;//Open the alarm
         case 0x44: openring=0;OPEN=1;break;//Turn off the alarm
         case 0x84:cancelring=1;break;//Cancel the ringing            
         default: break;
                       }
                   }
   else   scode=(scode<<1)|0x01;
              }
           }     
       } 
} 

  Note: The keyboard values ​​are encoded here. 12 keyboards are encoded. Pay special attention to the implementation methods of alarm setting and time setting. They share the function resettime, which is not difficult.      
void resettime (viod)  
{
 if(hour==1)
   {
     if (add==1)
        {hour1++;add=0;}

     if( hour1==24)
         hour1=0;

     if (dec==1)
         {hour1--;dec=0;}

     if (hour1==-1)
        hour1=23;
   }
  if(minutes==1)
  {
     if (add==1)
      {minutes1++;add=0;}

     if (minutes1==60)
         minutes1=0;

     if(dec==1)
      { minutes1--;dec=0;}

     if (minutes1==-1)
       minutes1=59;
   }

    if(second==1)
  { 
    if (add==1)
      {second1++;add=0;}

    if(second1==60)
      second1=0;

    if (dec==1)
      {second1--;dec=0;}

    if(second1==-1)
      second1=59;
   }

}
 
  

 display (void) //display function subroutine
{  
   flying j,n;
   for(n=0,j=0XFE;n<8;j=((j<<1)|0X01),n++)
     {P1=j; //P1 connects to digital tube position selection
      P0=LED[buffer[n]]; //P0 is connected to the digital tube segment selection
      delay_1ms(5);
     }
}


                          
 void main (void)
{ 
   inital(); // Call timer initialization
  for(;;)                           
  {                        
    timebcd(miao,fen,shi);  

    keyscan(); 
                                       //Call key scan and confirm function
    if(settime==1) //When the key pressed is time setting
      { 
          resettime();
   timebcd ( second1, minutes1,hour1);
 

          if(ok==1) //When the OK button is pressed, it indicates that the reset time will overwrite the original time, so reset miao, fen, shi, and clear _20ms to zero
           { shi=hour1;
      fen=minutes1;
      miao=second1;
             _20ms=0;
                                                  }
      } 

   if(setring==1)
   {   
      resettime();
      timebcd( second1, minutes1,hour1);

         if(ok==1)
           {  hour2=hour1;
       minutes2=minutes1;
       second2=second1;
                                                         }
      }

     display(); //Call display function

    }
}