Code in C

//#include <AT89Cstm.h> /* special function register declarations */
//#include <stdio.h>
#ifndef __REG52_H__
#define __REG52_H__

sfr DataPort = 0xA0; // Port 2

sfr p0 = 0x80;
sfr p1 = 0x90;
sfr p2 = 0xA0;
sfr p3 = 0xB0;

sbit Seg1 = 0x90; // Port 1 pin 0, Sec1
sbit Seg2 = 0x91; // Port 1 pin 1,
sbit Seg3 = 0x92; // Port 1 pin 2,
sbit Seg4 = 0x93; // Port 1 pin 3,
sbit Seg5 = 0x94; // Port 1 pin 4,
sbit Seg6 = 0x95; // Port 1 pin 5, Hor 2

sbit ShowTime = 0xb6; // port 0.6
sbit SetTime = 0xb7; // port 0.7

sbit PulseIn = 0xB2; // port 3.2

sbit IncrementPressed = 0x97; // port 3.3                Min or hor Increment
sbit DecrementPressed = 0x96; // port 3.4                Min or hor Decrement

sbit MINorHOr = 0xB5; // port 3.5                Min or hor selection

sbit SegHL = 0xB3; // Segment common High or Low port 3.2
sbit DataHL = 0xB4; // Segment Data High or Low

#endif



unsigned char sec=0,min=10,hour=15,day=1,mnth=1,year=2011;
unsigned char SegData[12] = {0x3F,0x06,0x5b,0x4f,0x66,0x6d,0x7d,0x07,0x7f,0x6f,0x00,0xB9};
                        //   0    1    2    3    4    5    6    7    8    9   blnk  C
                        //   gfedcba        gfedcba                                 hgfedcba
                        //   0111111        1001111        ..         ..      ..    10111001

bit SecStored = 0;
bit IncrementStored = 0;
bit DecrementStored = 0;
bit TimeStop = 0;
bit TimeSaved = 0;
bit SendData = 0;
unsigned char  SendCount = 0;
void ShowSec();
void ShowMin();
void ShowHour();
void IncSec();
void IncMin();
void IncHour();
//void DecSec();
void DecMin();
void DecHour();
void Delay();
void ScanSecond();
void ScanIncrement();
void ScanInputs();
void ScanDecrement();
void ScanDecrement();

void main()
   {
unsigned int temp=0;

p0 = 255;
p1 = 0;
p2 = 0;
p3 = 255;

while (temp !=1)
        {

                if (SetTime == 0 || ShowTime == 0)
                {
                        ShowSec();
                        ShowMin();
                        ShowHour();
                        if (SetTime == 0)
                        {
                                ScanIncrement();
                                ScanDecrement();
                        }
                }
                else
                {
                        if(TimeStop == 1)
                        {
                                TimeStop = 0;
                        }
                                p1 = 255;
                                p2 = 255;

                }
                ScanSecond();
        }
 }

void ScanSecond()
{
        if (PulseIn == 1 && SecStored == 0 && TimeStop == 0)  // Scan Second Pulse
        {
                IncSec();
                SecStored = 1;
        }
        else
        {
                if (PulseIn == 0 && SecStored == 1)
                {
                SecStored = 0;
                }
        }
}

void ScanIncrement()
{
        if (IncrementPressed == 0 && IncrementStored == 0 )  // Scan Increment Pulse
        {
                if (MINorHOr == 1 )
                {
                        IncMin();
                        SendData = 1;
                }
                else
                {
                        IncHour();
                        SendData = 1;
                }
                IncrementStored = 1;
                TimeStop = 1;
                sec = 0;
        }
        else
        {
                if (IncrementPressed == 1 && IncrementStored == 1)
                {
                IncrementStored = 0;
                }
        }
}

void ScanDecrement()
{
        if (DecrementPressed == 0 && DecrementStored == 0 )  // Scan Decrement Pulse
        {
                if (MINorHOr == 1 )
                {
                        DecMin();
                        SendData = 1;
                }
                else
                {
                        DecHour();
                        SendData = 1;
                }
                DecrementStored = 1;
                TimeStop = 1;
                sec = 0;
        }
        else
        {
                if (DecrementPressed == 1 && DecrementStored == 1)
                {
                DecrementStored = 0;
                }
        }
}



void ShowSec()
{
        Seg6 = (~SegHL);
        if(DataHL == 0)
                DataPort = SegData[sec % 10];
        else
                DataPort = (~(SegData[sec % 10]));
        Seg1 =  SegHL;
Delay();
        Seg1 = (~SegHL);
        if(DataHL == 0)
                DataPort = SegData[sec / 10];
        else
                DataPort = (~(SegData[sec / 10]));
        Seg2 =  SegHL;
Delay();
}

void ShowMin()
{
        Seg2 = (~SegHL);
        if(DataHL == 0)
                DataPort = SegData[min % 10];
        else
                DataPort = (~(SegData[min % 10]));
        Seg3 =  SegHL;
Delay();
        Seg3 = (~SegHL);
        if(DataHL == 0)
                DataPort = SegData[min / 10];
        else
                DataPort = (~(SegData[min / 10]));
        Seg4 =  SegHL;
Delay();
}

void ShowHour()
{
        Seg4 = (~SegHL);
        if(DataHL == 0)
                DataPort = SegData[hour % 10];
        else
                DataPort = (~(SegData[hour % 10]));
        Seg5 =  SegHL;
Delay();
        Seg5 = (~SegHL);
        if(DataHL == 0)
                DataPort = SegData[hour / 10];
        else
                DataPort = (~(SegData[hour / 10]));
        Seg6 =  SegHL;
Delay();
}

void IncSec()
{
sec = sec + 1;
if(sec==60)
        {
        sec = 0;
        if (SetTime == 1 )
        IncMin();
        }
}

void IncMin()
{
min = min + 1;
if(min==60)
        {
        min=0;
        if (SetTime == 1 )
        IncHour();
        }
}

void IncHour()
{
hour = hour + 1;
if(hour==24)
        {
        hour = 0;
        //IncHour();
        }
}
/*
void DecSec()
{
sec = sec - 1;
if(sec==255)
        {
        sec = 59;
        if (SetTime == 1 )
        DecMin();
        }
}
  */
void DecMin()
{
min = min - 1;
if(min==255)
        {
        min=59;
        if (SetTime == 1 )
        DecHour();
        }
}

void DecHour()
{
hour = hour - 1;
if(hour==255)
        {
        hour = 23;
        //IncHour();
        }
}

void Delay()
   {
  unsigned int i;
        for(i=0; i<100; i++)
  {
  }

   }