//Connect FOUR 7-Segment Displays to 4 individual ports
//Display a clock (Min & Sec only).

#include "register.h"
#include "functions.h"

#define SEC_LOWER_LIMIT 00
#define SEC_UPPER_LIMIT 59

#define MIN_LOWER_LIMIT 00
#define MIN_UPPER_LIMIT 59

void setup()
{
  /*Display 3 is connected to PORTF.
    Display 2 is connected to PORTK.
    Display 1 is connected to PORTA.
    Display 0 is connected to PORTC.*/

  *dirf = 0xFF;//set PORT F as o/p port .
  *dirk = 0xFF;//set PORT K as o/p port .
  *dira = 0xFF;//set PORT F as o/p port .
  *dirc = 0xFF;//set PORT K as o/p port .

  int i, k;
  volatile long j = 0;
  int digits[5];

  while (1)
  {
    for (i = MIN_LOWER_LIMIT; i <= MIN_UPPER_LIMIT; i++)
    {
      for ( k = SEC_LOWER_LIMIT; k <= SEC_UPPER_LIMIT; k++)
      {
        int digits[] = {(int)(k % 10), //ones digit of seconds
                        (int)(k / 10), //tens degit of seconds
                        (int)(i % 10), //ones digit of minutes
                        (int)(i / 10) //tens degit of minutes
                       };
        *outc = display(digits[0]);
        *outa = display(digits[1]);
        *outk = display_with_dp(digits[2]);
        *outf = display(digits[3]);
        for (j = 0; j < 625000; j++);//delay for the display
      }
    }
  }
}


sketch.ino

diagram.json

  volatile char *dirf = (char*)0x30;//DDRF – Port F Data Direction Register
  volatile char *dirk = (char*)0x107;//DDRK – Port K Data Direction Register
  volatile char *dira = (char*)0x21;//DDRA – Port F Data Direction Register
  volatile char *dirc = (char*)0x27;//DDRC – Port K Data Direction Register
  volatile char *outf = (char*)0x31;//PORTF – Port F Data Register
  volatile char *outk = (char*)0x108;//PORTK – Port F Data Register
  volatile char *outa = (char*)0x22;//PORTA – Port F Data Register
  volatile char *outc = (char*)0x28;//PORTC – Port F Data Register

register.h

// display function is used to display numbers 0 to 9 on a seven segment display
int display(int num)
{
  long int x;
  long seven_segment[] = {0x3F,//0
                          0x06,//1
                          0x5B,//2
                          0x4F,//3
                          0x66,//4
                          0x6D,//5
                          0x7D,//6
                          0x07,//7
                          0x7F,//8
                          0x67//9
                         };
  x = seven_segment[num];
  return x;
}

//display_with_dp() is used to display numbers 0 to 9 with dot pointer on a seven segment display
int display_with_dp(int num)
{
  long int x;
  long seven_segment[] = {0xBF, //0.
                          0x86,//1.
                          0xDB,//2.
                          0xCF,//3.
                          0xE6,//4.
                          0xED,//5.
                          0xFD,//6.
                          0x87,//7.
                          0xFF,//8.
                          0xE7,//9.
                         };
  x = seven_segment[num];
  return x;
}