Arduino Library for Maxim Integrated DS3232 and DS3231 Real-Time Clocks
C++
Latest commit 80a33b3 Oct 24, 2015 @JChristensen Use /64 instead of >>6 to right-justify the temperature value from the
DS323x register. Using GCC, the two methods are equivalent but the C++ standard
says that this behavior for the right shift is implementation-specific.
Closes #16.

ReadMe.md

Arduino DS3232RTC Library v1.0

https://github.com/JChristensen/DS3232RTC ReadMe file
Jack Christensen Mar 2013

CC BY-SA

Introduction

DS3232RTC is an Arduino library that supports the Maxim Integrated DS3232 and DS3231 Real-Time Clocks. This library is intended to be used with the Arduino Time library.

The DS3232RTC library is a drop-in replacement for the DS1307RTC.h library by Michael Margolis that is supplied with the Arduino Time library above. To change from using a DS1307 RTC to an DS323x RTC, it is only necessary to use #include <DS3232RTC.h> instead of #include <DS1307RTC.h>.

This library is not a drop-in replacement for PJRC's newer version of the DS1307RTC library.

DS3232RTC also implements functions to support the additional features of the DS3232 and DS3231. The DS3231 has the same features as the DS3232 except: (1) Battery-backed SRAM, (2) Battery-backed 32kHz output (BB32kHz bit in Control/Status register 0x0F), and (3) Adjustable temperature sensor sample rate (CRATE1:0 bits in the Control/Status register).

"Arduino DS3232RTC Library" by Jack Christensen is licensed under CC BY-SA 4.0.

Installation

To use the DS3232RTC library:

  • Go to https://github.com/JChristensen/DS3232RTC, click the Download ZIP button and save the ZIP file to a convenient location on your PC.
  • Uncompress the downloaded file. This will result in a folder containing all the files for the library, that has a name that includes the branch name, usually DS3232RTC-master.
  • Rename the folder to just DS3232RTC.
  • Copy the renamed folder to the Arduino sketchbook\libraries folder.

Examples

The following example sketches are included with the DS3232RTC library:

  • SetSerial: Set the RTC's date and time from the Arduino serial monitor. Displays date, time and temperature.
  • TimeRTC: Same as the example of the same name provided with the Time library, demonstrating the interchangeability of the DS3232RTC library with the DS1307RTC library.
  • tiny3232_KnockBang: Demonstrates interfacing an ATtiny45/85 to a DS3231 or DS3232 RTC.

Usage notes

When using the DS3232RTC library, the user is responsible for ensuring that reads and writes do not exceed the device's address space (0x00-0x12 for DS3231, 0x00-0xFF for DS3232); no bounds checking is done by the library.

Similar to the DS1307RTC library, the DS3232RTC library instantiates an RTC object; the user does not need to do this.

To use the DS3232RTC library, the Time and Wire libraries must also be included. For brevity, these includes are not repeated in the examples below:

#include <DS3232RTC.h>    //http://github.com/JChristensen/DS3232RTC
#include <Time.h>         //http://www.arduino.cc/playground/Code/Time
#include <Wire.h>         //http://arduino.cc/en/Reference/Wire (included with Arduino IDE)

Enumerations

SQWAVE_FREQS_t

Description

Symbolic names used with the squareWave() method (described below).

Values
  • SQWAVE_NONE
  • SQWAVE_1_HZ
  • SQWAVE_1024_HZ
  • SQWAVE_4096_HZ
  • SQWAVE_8192_HZ

ALARM_TYPES_t

Description

Symbolic names used with the setAlarm() method (described below).

Values for Alarm 1
  • ALM1_EVERY_SECOND -- causes an alarm once per second.
  • ALM1_MATCH_SECONDS -- causes an alarm when the seconds match (i.e. once per minute).
  • ALM1_MATCH_MINUTES -- causes an alarm when the minutes and seconds match.
  • ALM1_MATCH_HOURS -- causes an alarm when the hours and minutes and seconds match.
  • ALM1_MATCH_DATE -- causes an alarm when the date of the month and hours and minutes and seconds match.
  • ALM1_MATCH_DAY -- causes an alarm when the day of the week and hours and minutes and seconds match.
Values for Alarm 2
  • ALM2_EVERY_MINUTE -- causes an alarm once per minute.
  • ALM2_MATCH_MINUTES -- causes an alarm when the minutes match (i.e. once per hour).
  • ALM2_MATCH_HOURS -- causes an alarm when the hours and minutes match.
  • ALM2_MATCH_DATE -- causes an alarm when the date of the month and hours and minutes match.
  • ALM2_MATCH_DAY -- causes an alarm when the day of the week and hours and minutes match.

Methods for setting and reading the time

get(void)

Description

Reads the current date and time from the RTC and returns it as a time_t value. Returns zero if an I2C error occurs (RTC not present, etc.).

Syntax

RTC.get();

Parameters

None.

Returns

Current date and time (time_t)

Example
time_t myTime;
myTime = RTC.get();

set(time_t t)

Description

Sets the RTC date and time to the given time_t value. Clears the oscillator stop flag (OSF) bit in the control/status register. See the oscStopped() function and also the DS323x datasheet for more information on the OSF bit.

Syntax

RTC.set(t);

Parameters

t: The date and time to set the RTC to (time_t)

Returns

I2C status (byte). Returns zero if successful.

Example
//this example first sets the system time (maintained by the Time library) to
//a hard-coded date and time, and then sets the RTC from the system time.
//the setTime() function is part of the Time library.
setTime(23, 31, 30, 13, 2, 2009);   //set the system time to 23h31m30s on 13Feb2009
RTC.set(now());                     //set the RTC from the system time

read(tmElements_t &tm)

Description

Reads the current date and time from the RTC and returns it as a tmElements_t structure. See the Arduino Time library for details on the tmElements_t structure.

Syntax

RTC.read(tm);

Parameters

tm: Address of a tmElements_t structure to which the date and time are returned.

Returns

I2C status (byte). Returns zero if successful. The date and time read from the RTC are returned to the tm parameter.

Example
tmElements_t tm;
RTC.read(tm);
Serial.print(tm.Hour, DEC);
Serial.print(':');
Serial.print(tm.Minute,DEC);
Serial.print(':');
Serial.println(tm.Second,DEC);

write(tmElements_t &tm)

Description

Sets the RTC to the date and time given by a tmElements_t structure. Clears the oscillator stop flag (OSF) bit in the control/status register. See the oscStopped() function and also the DS323x datasheet for more information on the OSF bit.

Syntax

RTC.write(tm);

Parameters

tm: Address of a tmElements_t structure used to set the date and time.

Returns

I2C status (byte). Returns zero if successful.

Example
tmElements_t tm;
tm.Hour = 23;             //set the tm structure to 23h31m30s on 13Feb2009
tm.Minute = 31;
tm.Minute = 30;
tm.Day = 13;
tm.Month = 2;
tm.Year = 2009 - 1970;    //tmElements_t.Year is the offset from 1970
RTC.write(tm);            //set the RTC from the tm structure

Methods for reading and writing RTC registers or static RAM (SRAM) for the DS3232

The DS3232RTC.h file defines symbolic names for the timekeeping, alarm, status and control registers. These can be used for the addr argument in the functions below.

writeRTC(byte addr, byte *values, byte nBytes)

Description

Write one or more bytes to RTC memory.

Syntax

RTC.writeRTC(addr, values, nbytes);

Parameters

addr: First SRAM address to write (byte). The valid address range is 0x00-0x12 for DS3231, 0x00-0xFF for DS3232. The general-purpose SRAM for the DS3232 begins at address 0x14. Address is not checked for validity by the library. values: An array of values to write (*byte)
nBytes: Number of bytes to write (byte). Must be between 1 and 31 (Wire library limitation) but is not checked by the library.

Returns

I2C status (byte). Returns zero if successful.

Example
//write 1, 2, ..., 8 to the first eight DS3232 SRAM locations
byte buf[8] = {1, 2, 3, 4, 5, 6, 7, 8};
RTC.sramWrite(0x14, buf, 8);

writeRTC(byte addr, byte value)

Description

Write a single byte to RTC memory.

Syntax

RTC.writeRTC(addr, value);

Parameters

addr: SRAM address to write (byte). The valid address range is 0x00-0x12 for DS3231, 0x00-0xFF for DS3232. The general-purpose SRAM for the DS3232 begins at address 0x14. Address is not checked for validity by the library. value: Value to write (byte)

Returns

I2C status (byte). Returns zero if successful.

Example
RTC.writeRTC(3, 14);   //write the value 14 to SRAM address 3

readRTC(byte addr, byte *values, byte nBytes)

Description

Read one or more bytes from RTC RAM.

Syntax

RTC.readRTC(addr, values, nbytes);

Parameters

addr: First SRAM address to read (byte). The valid address range is 0x00-0x12 for DS3231, 0x00-0xFF for DS3232. The general-purpose SRAM for the DS3232 begins at address 0x14. Address is not checked for validity by the library. values: An array to receive the values read (*byte)
nBytes: Number of bytes to read (byte). Must be between 1 and 32 (Wire library limitation) but is not checked by the library.

Returns

I2C status (byte). Returns zero if successful.

Example
//read the last eight locations of SRAM into buf
byte buf[8];
RTC.sramRead(248, buf, 8);

readRTC(byte addr)

Description

Reads a single byte from RTC RAM.

Syntax

RTC.readRTC(addr);

Parameters

addr: SRAM address to read (byte). The valid address range is 0x00-0x12 for DS3231, 0x00-0xFF for DS3232. The general-purpose SRAM for the DS3232 begins at address 0x14. Address is not checked for validity by the library.

Returns

Value read from the RTC (byte)

Example
byte val;
val = RTC.readRTC(3);  //read the value from SRAM location 3

Alarm methods

The DS3232 and DS3231 have two alarms. Alarm1 can be set to seconds precision; Alarm2 can only be set to minutes precision.

setAlarm(ALARM_TYPES_t alarmType, byte seconds, byte minutes, byte hours, byte daydate)

Description

Set an alarm time. Sets the alarm registers only. To cause the INT pin to be asserted on alarm match, use alarmInterrupt(). This method can set either Alarm 1 or Alarm 2, depending on the value of alarmType (use the ALARM_TYPES_t enumeration above). When setting Alarm 2, the seconds value must be supplied but is ignored, recommend using zero. (Alarm 2 has no seconds register.)

Syntax

RTC.setAlarm(alarmType, seconds, minutes, hours, dayOrDate);

Parameters

alarmType: A value from the ALARM_TYPES_t enumeration, above. (ALARM_TYPES_t)
seconds: The seconds value to set the alarm to. (byte)
minutes: The minutes value to set the alarm to. (byte)
hours: The hours value to set the alarm to. (byte)
dayOrDate: The day of the week or the date of the month. For day of the week, use a value from the Time library timeDayOfWeek_t enumeration, i.e. dowSunday, dowMonday, dowTuesday, dowWednesday, dowThursday, dowFriday, dowSaturday. (byte)

Returns

None.

Example
//Set Alarm1 for 12:34:56 on Sunday
RTC.setAlarm(ALM1_MATCH_DAY, 56, 34, 12, dowSunday);

setAlarm(ALARM_TYPES_t alarmType, byte minutes, byte hours, byte daydate)

Description

Set an alarm time. Sets the alarm registers only. To cause the INT pin to be asserted on alarm match, use alarmInterrupt(). This method can set either Alarm 1 or Alarm 2, depending on the value of alarmType (use the ALARM_TYPES_t enumeration above). However, when using this method to set Alarm 1, the seconds value is set to zero. (Alarm 2 has no seconds register.)

Syntax

RTC.setAlarm(alarmType, minutes, hours, dayOrDate);

Parameters

alarmType: A value from the ALARM_TYPES_t enumeration, above. (ALARM_TYPES_t)
minutes: The minutes value to set the alarm to. (byte)
hours: The hours value to set the alarm to. (byte)
dayOrDate: The day of the week or the date of the month. For day of the week, use a value from the Time library timeDayOfWeek_t enumeration, i.e. dowSunday, dowMonday, dowTuesday, dowWednesday, dowThursday, dowFriday, dowSaturday. (byte)

Returns

None.

Example
//Set Alarm2 for 12:34 on the 4th day of the month
RTC.setAlarm(ALM1_MATCH_DATE, 34, 12, 4);

alarmInterrupt(byte alarmNumber, boolean alarmEnabled)

Description

Enable or disable an alarm "interrupt". Note that this "interrupt" causes the RTC's INT pin to be asserted. To use this signal as an actual interrupt to a microcontroller, it will need to be connected properly and programmed in the application firmware. on the RTC.

Syntax

RTC.alarmInterrupt(alarmNumber, enable);

Parameters

alarmNumber: The number of the alarm to enable or disable, ALARM_1 or ALARM_2 (byte)
alarmEnabled: true or false (boolean)

Returns

None.

Example
RTC.alarmInterrupt(ALARM_1, true);      //assert the INT pin when Alarm1 occurs.
RTC.alarmInterrupt(ALARM_2, false);     //disable Alarm2

alarm(byte alarmNumber)

Description

Tests whether an alarm has been triggered. If the alarm was triggered, returns true and resets the alarm flag in the RTC, else returns false.

Syntax

RTC.alarm(alarmNumber);

Parameters

alarmNumber: The number of the alarm to test, ALARM_1 or ALARM_2 (byte)

Returns

Description (type)

Example
if ( RTC.alarm(ALARM_1) ) {     //has Alarm1 triggered?
    //yes, act on the alarm
}
else {
    //no alarm
}

Other methods

temperature(void)

Description

Returns the RTC temperature.

Syntax

RTC.temperature();

Parameters

None.

Returns

RTC temperature as degrees Celsius times four. (int)

Example
int t = RTC.temperature();
float celsius = t / 4.0;
float fahrenheit = celsius * 9.0 / 5.0 + 32.0;

squareWave(SQWAVE_FREQS_t freq)

Description

Enables or disables the square wave output.

Syntax

RTC.squareWave(freq);

Parameters

freq: a value from the SQWAVE_FREQS_t enumeration above. (SQWAVE_FREQS_t)

Returns

None.

Example
RTC.squareWave(SQWAVE_1_HZ);    //1 Hz square wave
RTC.squareWave(SQWAVE_NONE);    //no square wave

oscStopped(bool clearOSF)

Description

Returns the value of the oscillator stop flag (OSF) bit in the control/status register which indicates that the oscillator is or was stopped, and that the timekeeping data may be invalid. Optionally clears the OSF bit depending on the argument passed. If the clearOSF argument is omitted, the OSF bit is cleared by default. Calls to set() and write() also clear the OSF bit.

Syntax

RTC.oscStopped(clearOSF);

Parameters

clearOSF: an optional true or false value to indicate whether the OSF bit should be cleared (reset). If not supplied, a default value of true is used, resetting the OSF bit. (bool)

Returns

True or false (bool)

Example
if ( RTC.oscStopped(false) ) {      //check the oscillator
    //may be trouble
}
else {
    //all is well
}