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DS1337 RTC Driver

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Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

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DS1337 RTC Driver
PostPosted: Mon Oct 02, 2006 8:57 am     Reply with quote

Here is a driver for the Maxim DS1337 I2C RTC. This is PCM Programmer's PCF8583 driver code from post:

That has been modified for the DS1337. The basic functionality has been tested but I can't guarantee that it's 100% error free. I will edit the post with any bug corrections.

The DS1337 is good solution for a simple and small RTC that has alarms, although it may be hard to find.

Version1 10/02/06


// DS1337.H

/* ---------------------------------------------
Use the following lines or declare in application.

#ifndef DS1337_SDA
#define DS1337_SDA  PIN_C4
#define DS1337_SCL  PIN_C3

#use i2c(master, sda=DS1337_SDA, scl=DS1337_SCL)

// i2c addresses
#define DS1337_I2C_WRITE_ADDR    0xD0
#define DS1337_I2C_READ_ADDR     0xD1

// DS1337 register addresses
#define DS1337_SECONDS_REG       0x00
#define DS1337_MINUTES_REG       0x01
#define DS1337_HOURS_REG         0x02
#define DS1337_DAY_OF_WEEK_REG   0x03
#define DS1337_DATE_REG          0x04
#define DS1337_MONTH_REG         0x05
#define DS1337_YEAR_REG          0x06
//DS1337 Unique Registers
#define DS1337_ALM1_SECONDS_REG  0x07
#define DS1337_ALM1_MINUTES_REG  0x08
#define DS1337_ALM1_HOURS_REG    0x09
#define DS1337_ALM1_DAYDATE_REG  0x0A
#define DS1337_ALM2_MINUTES_REG  0x0B
#define DS1337_ALM2_HOURS_REG    0x0C
#define DS1337_ALM2_DAYDATE_REG  0x0D
#define DS1337_CONTROL_REG       0x0E
#define DS1337_STATUS_REG        0x0F

//Enable Oscillator, Disable SQWV, Disable Ints
#define DS1337_CTRL_REG_INIT_VAL 0x04

//Clear OSF (Oscillator Stop Flag), A2F (Alarm 2 Flag), and A1F (Alarm 1 Flag)
#define DS1337_CLEAR_STATUS_VAL  0x00

char const weekday_names[7][4] = {  {"Sun"},
                                    {"Sat"} };

// This structure defines the user's date and time data.
// The values are stored as unsigned integers.  The user
// should declare a structure of this type in the application
// program. Then the address of the structure should be
// passed to the DS1337 read/write functions in this
// driver, whenever you want to talk to the chip.
typedef struct {
   int8 seconds;    // 0 to 59
   int8 minutes;    // 0 to 59
   int8 hours;      // 0 to 23  (24-hour time)
   int8 day;        // 0 = Sunday, 1 = Monday, etc.
   int8 date;       // 1 to 31
   int8 month;      // 1 to 12
   int8 year;       // 00 to 99
} date_time_t;

void DS1337_write_byte(int8 address, int8 data) {





int8 DS1337_read_byte(int8 address) {

   int8 retval;

   retval = i2c_read(0);


// This function converts an 8 bit binary value
// to an 8 bit BCD value.
// The input range must be from 0 to 99.

int8 bin2bcd(int8 value) {

   char retval;
   retval = 0;

      // Get the tens digit by doing multiple subtraction
      // of 10 from the binary value.
      if(value >= 10)
         value -= 10;
         retval += 0x10;
      else // Get the ones digit by adding the remainder.
         retval += value;



// This function converts an 8 bit BCD value to
// an 8 bit binary value.
// The input range must be from 00 to 99.

char bcd2bin(char bcd_value) {

   char temp;

   temp = bcd_value;

   // Shifting the upper digit right by 1 is
   // the same as multiplying it by 8.
   temp >>= 1;

   // Isolate the bits for the upper digit.
   temp &= 0x78;

   // Now return: (Tens * 8) + (Tens * 2) + Ones
   return(temp + (temp >> 2) + (bcd_value & 0x0f));


void DS1337_set_datetime(date_time_t *dt) {

   int8 bcd_sec;
   int8 bcd_min;
   int8 bcd_hrs;
   int8 bcd_day;
   int8 bcd_date;
   int8 bcd_mon;
   int8 bcd_year;

   // Convert the input date/time into BCD values
   // that are formatted for the DS1337 registers.
   bcd_sec  = bin2bcd(dt->seconds);
   bcd_min  = bin2bcd(dt->minutes);
   bcd_hrs  = bin2bcd(dt->hours);    //default to 24 hour mode
   bcd_day  = bin2bcd(dt->day);
   bcd_date = bin2bcd(dt->date);
   bcd_mon  = bin2bcd(dt->month);    //ignore century bit
   bcd_year = bin2bcd(dt->year);

   // Write to the date and time registers.  Disable interrupts
   // so they can't disrupt the i2c operations.

   i2c_write(DS1337_SECONDS_REG);   // Start at seconds register



// Read the Date and Time from the hardware registers
// in the DS1337.
void DS1337_read_datetime(date_time_t *dt) {

   int8 bcd_sec;
   int8 bcd_min;
   int8 bcd_hrs;
   int8 bcd_day;
   int8 bcd_date;
   int8 bcd_mon;
   int8 bcd_year;

   // Disable interrupts so the i2c process is not disrupted.

   // Read the date/time registers from the DS1337.
   i2c_write(DS1337_SECONDS_REG);   // Start at seconds register

   bcd_sec  = i2c_read();
   bcd_min  = i2c_read();
   bcd_hrs  = i2c_read();
   bcd_day  = i2c_read();
   bcd_date = i2c_read();
   bcd_mon  = i2c_read();
   bcd_year = i2c_read(0);


   // Convert the date/time values from BCD to
   // unsigned 8-bit integers. Unpack bits in
   // DS1337 registers where required.
   dt->seconds = bcd2bin(bcd_sec  & 0x7F);
   dt->minutes = bcd2bin(bcd_min  & 0x7F);
   dt->hours   = bcd2bin(bcd_hrs  & 0x3F);
   dt->day     = bcd2bin(bcd_day  & 0x07);
   dt->date    = bcd2bin(bcd_date & 0x3F);
   dt->month   = bcd2bin(bcd_mon  & 0x1F);
   dt->year    = bcd2bin(bcd_year);


//If there has been an oscillator failure since last
//init, then init DS1337. A default time and date is set as well.
void DS1337_init(void) {

    int8 temp = 0;

    //Read the status register to see if the oscillator has failed.
    temp = DS1337_read_byte(DS1337_STATUS_REG);
    //Unpack OSF bit
    temp = temp >> 7;

    //If oscillator has failed then init DS1337
    if(temp) {
      i2c_write(0x00);                     //seconds
      i2c_write(0x00);                     //minutes
      i2c_write(0x40);                     //hours & 12/24 hour mode
      i2c_write(0x00);                     //day
      i2c_write(0x01);                     //date
      i2c_write(0x01);                     //month
      i2c_write(0x06);                     //year
      i2c_write(0x00);                     //alm1 seconds
      i2c_write(0x00);                     //alm1 minutes
      i2c_write(0x00);                     //alm1 hours
      i2c_write(0x00);                     //alm1 day/date
      i2c_write(0x00);                     //alm2 minutes
      i2c_write(0x00);                     //alm2 hours
      i2c_write(0x00);                     //alm2 day/date
      i2c_write(DS1337_CTRL_REG_INIT_VAL); //Turn off the squarewave output pin.
      i2c_write(DS1337_CLEAR_STATUS_VAL);  //Clear the status registers
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