void display(volatile unsigned char* out,volatile unsigned char* digit,char thousands,char hundreds,char tens,char ones);
char seven_segment_code(char num, char decimal);
volatile char read_keypad(volatile unsigned char* in_key,volatile unsigned char* out_key);



int main()
{
  volatile char* dir;

  dir = 0x30;
  *dir = 0x0F;

  dir = 0x107;
  *dir = 0xFF;

  dir = 0x27;
  *dir = 0xFF;

  volatile unsigned char* out_key;
  volatile unsigned char* in_key;
  volatile unsigned char* out_display;
  volatile unsigned char* out_display_picker;
  volatile char data,i,sum;
  volatile char num[4];

  out_key = 0x31;
  in_key = 0x2F;
  
  out_display = 0x108;
  out_display_picker = 0x28;
 
  i=0;
  sum = 0;

  while(1)
  {
    data = read_keypad(in_key,out_key);

    if(data!=-1 && i!=2)
    {
      sum = data+sum;
      i++;

      while(data!=-1)
      {
        data = read_keypad(in_key,out_key);
      }
    }
    else if(i == 2)
    {
      display(out_display,out_display_picker,(sum/1000)%10,(sum/100)%10,(sum/10)%10,(sum)%10);
    }
    
  }

}

void display(volatile unsigned char* out,volatile unsigned char* window,char thousands,char hundreds,char tens,char ones)
{
  //ones
  *window = ~(0x01);
  *out = seven_segment_code(ones,0);
  for(volatile long i = 0;i<10000;i++);
  *out = 0x00;

  //tens
  *window = ~(0x01<<1);
  *out = seven_segment_code(tens,0);
  for(volatile long i = 0;i<10000;i++);
  *out = 0x00;

  //hundreds
  *window = ~(0x01<<2);
  *out = seven_segment_code(hundreds,0);
  for(volatile long i = 0;i<10000;i++);
  *out = 0x00;

  //thousands
  *window = ~(0x01<<3);
  *out = seven_segment_code(thousands,0);
  for(volatile long i =0;i<10000;i++);
  *out = 0x00;
}

char seven_segment_code(char num, char decimal)
{
  char temp;
  switch(num)
  {
    case 0:
      temp = 0x3F;
      break;
    case 1:
      temp = 0x06;
      break;
    case 2:
      temp = 0x5B;
      break;
    case 3:
      temp = 0x4F;
      break;
    case 4:
      temp = 0x66;
      break;
    case 5:
      temp = 0x6D;
      break;
    case 6:
      temp = 0x7D;
      break;
    case 7:
      temp = 0x07;
      break;
    case 8:
      temp = 0X7F;
      break;
    case 9:
      temp = 0x6F;
      break; 
  }

  if(decimal == 0)
  {
      ;
  }
  else if(decimal == 1)
  {
    temp = temp + 128;
  }

  return(temp);
}

volatile char read_keypad(volatile unsigned char* in_key,volatile unsigned char* out_key)
{
  volatile char matrix[4][4] = {1,2,3,'A',4,5,6,'B',7,8,9,'C','*',0,'#','D'};

  char i;

  volatile unsigned char temp;
  volatile char count;

  for(volatile long i = 0;i<5000;i++); //debouncing

  for(i=0;i<4;i++)
  {
    temp = 0x10;
    *out_key = 0x01<<i;

    if(((*in_key)&0xF0)!=0x00)  //the expression inside is for masking
    {
      count = 0;
      while(((*in_key)&0xF0)!=temp) //to convert to a number
      {
        temp = temp<<1;
        count++;
      }

      return(matrix[i][count]);
    }
  }

  return -1; // << optional

}