Real Time Clock (DS1307)

[Ogbonnia Dumken Chibundu]

Good Day Guys. Pls can anyone help me explain this part of this code. I've gone through the register in the data sheet but still confused. The coloured part is the problem.

// LCD module connections
sbit LCD_RS at RB2_bit;
sbit LCD_EN at RB3_bit;
sbit LCD_D4 at RB4_bit;
sbit LCD_D5 at RB5_bit;
sbit LCD_D6 at RB6_bit;
sbit LCD_D7 at RB7_bit;

sbit LCD_RS_Direction at TRISB2_bit;
sbit LCD_EN_Direction at TRISB3_bit;
sbit LCD_D4_Direction at TRISB4_bit;
sbit LCD_D5_Direction at TRISB5_bit;
sbit LCD_D6_Direction at TRISB6_bit;
sbit LCD_D7_Direction at TRISB7_bit;
// End LCD module connections



unsigned short read_ds1307(unsigned short address)
{
  unsigned short r_data;
  I2C1_Start();
  I2C1_Wr(0xD0); //address 0x68 followed by direction bit (0 for write, 1 for read) 0x68 followed by 0 --> 0xD0
  I2C1_Wr(address);
  I2C1_Repeated_Start();
  I2C1_Wr(0xD1); //0x68 followed by 1 --> 0xD1
  r_data=I2C1_Rd(0);
  I2C1_Stop();
  return(r_data);
}


void write_ds1307(unsigned short address,unsigned short w_data)
{
  I2C1_Start(); // issue I2C start signal
  //address 0x68 followed by direction bit (0 for write, 1 for read) 0x68 followed by 0 --> 0xD0
  I2C1_Wr(0xD0); // send byte via I2C (device address + W)
  I2C1_Wr(address); // send byte (address of DS1307 location)
  I2C1_Wr(w_data); // send data (data to be written)
  I2C1_Stop(); // issue I2C stop signal
}


unsigned char BCD2UpperCh(unsigned char bcd)
{
  return ((bcd >> 4) + '0');
}


unsigned char BCD2LowerCh(unsigned char bcd)
{
  return ((bcd & 0x0F) + '0');
}


int Binary2BCD(int a)
{
   int t1, t2;
   t1 = a%10;
   t1 = t1 & 0x0F;
   a = a/10;
   t2 = a%10;
   t2 = 0x0F & t2;
   t2 = t2 << 4;
   t2 = 0xF0 & t2;
   t1 = t1 | t2;
   return t1;
}


int BCD2Binary(int a)
{
   int r,t;
   t = a & 0x0F;
   r = t;
   a = 0xF0 & a;
   t = a >> 4;
   t = 0x0F & t;
   r = t*10 + r;
   return r;
}

int second;
int minute;
int hour;
int hr;
int day;
int dday;
int month;
int year;
int ap;

unsigned short set_count = 0;
short set;

char time[] = "00:00:00 PM";
char date[] = "00-00-00";

void main()
{
   I2C1_Init(100000); //DS1307 I2C is running at 100KHz

   CMCON = 0x07;   // To turn off comparators
   ADCON1 = 0x06;  // To turn off analog to digital converters

   TRISA = 0x07;
   PORTA = 0x00;

   Lcd_Init();                        // Initialize LCD
   Lcd_Cmd(_LCD_CLEAR);               // Clear display
   Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off
   Lcd_out(1,1,"Time:");
   Lcd_out(2,1,"Date:");
   
   do
   {
     set = 0;
     if(PORTA.F0 == 0)
     {
         Delay_ms(100);
         if(PORTA.F0 == 0)
         {
             set_count++;
             if(set_count >= 7)
             {
                set_count = 0;
             }
         }
     }
     if(set_count)
     {
        if(PORTA.F1 == 0)
        {
          Delay_ms(100);
          if(PORTA.F1 == 0)
              set = 1;
        }
        
        if(PORTA.F2 == 0)
        {
          Delay_ms(100);
          if(PORTA.F2 == 0)
              set = -1;
        }
        if(set_count && set)
        {
         [COLOR="#FF0000"] switch(set_count)
          {
            case 1:
                    hour = BCD2Binary(hour);
                    hour = hour + set;
                    hour = Binary2BCD(hour);
                    if((hour & 0x1F) >= 0x13)
                    {
                      hour = hour & 0b11100001;
                      hour = hour ^ 0x20;
                    }
                    else if((hour & 0x1F) <= 0x00)
                    {
                      hour = hour | 0b00010010;
                      hour = hour ^ 0x20;
                    }
                    write_ds1307(2, hour); //write hour
                    break;[/COLOR]
            case 2:
                     minute = BCD2Binary(minute);
                     minute = minute + set;
                     if(minute >= 60)
                        minute = 0;
                     if(minute < 0)
                        minute = 59;
                     minute = Binary2BCD(minute);
                     write_ds1307(1, minute); //write min
                     break;
            case 3:
                    if(abs(set))
                      write_ds1307(0,0x00); //Reset second to 0 sec. and start Oscillator
                    break;
            case 4:
                     day = BCD2Binary(day);
                     day = day + set;
                     day = Binary2BCD(day);
                     if(day >= 0x32)
                        day = 1;
                     if(day <= 0)
                        day = 0x31;
                     write_ds1307(4, day); // write date 17
                     break;
            case 5:
                    month = BCD2Binary(month);
                    month = month + set;
                    month = Binary2BCD(month);
                    if(month > 0x12)
                      month = 1;
                    if(month <= 0)
                      month = 0x12;
                    write_ds1307(5,month); // write month 6 June
                    break;
            case 6:
                    year = BCD2Binary(year);
                    year = year + set;
                    year = Binary2BCD(year);
                    if(year <= -1)
                       year = 0x99;
                    if(year >= 0x50)
                       year = 0;
                    write_ds1307(6, year); // write year
                    break;
          }
        }
     }

      second = read_ds1307(0);
      minute = read_ds1307(1);
      hour = read_ds1307(2);
       hr = hour & 0b00011111;
       ap = hour & 0b00100000;
      dday = read_ds1307(3);
      day = read_ds1307(4);
      month = read_ds1307(5);
      year = read_ds1307(6);


      time[0] = BCD2UpperCh(hr);
      time[1] = BCD2LowerCh(hr);
      time[3] = BCD2UpperCh(minute);
      time[4] = BCD2LowerCh(minute);
      time[6] = BCD2UpperCh(second);
      time[7] = BCD2LowerCh(second);

      date[0] = BCD2UpperCh(day);
      date[1] = BCD2LowerCh(day);
      date[3] = BCD2UpperCh(month);
      date[4] = BCD2LowerCh(month);
      date[6] = BCD2UpperCh(year);
      date[7] = BCD2LowerCh(year);
      
      if(ap)
      {
         time[9] = 'P';
         time[10] = 'M';
      }
      else
      {
         time[9] = 'A';
         time[10] = 'M';
      }

      
      Lcd_out(1, 6, time);
      Lcd_out(2, 6, date);
      Delay_ms(100);

   
   }while(1);
}

 

[milan.rajik]

Set button can be used to select between hours, minutes, day, month and year. It cycles between selecting these parameters on repeated presses. When set_count == 1 then case 1 of switch statement will be executed which is for setting hours of RTC. hour register contains the data read from RTC. RTC gives BCD data. So, hours data will be in BCD. It is converted to Decimal using BCD to Binary function. After hour is incremented it is converted to BCD form and stored in the same variable. Then there is some masking operations to check whether hours is in 24 hour mode or 12 hour mode. Finally hours value is written to hours register of RTC.

With masking proper bits of hours variable is set so that if 24 hour mode it writes hours variable to RTC hours register in 24 hour format. Similar method applies if 12 hour mode is selected. AM, PM bit has to be written to hours register if it is in 12 hour mode.

Post the circuit. To answer why

hour = hour + set;

is used we have to see the circuit.