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

Arduino DS3232RTC Library Copyright (C) 2018 Jack Christensen GNU GPL v3.0

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License v3.0 as published by the Free Software Foundation.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see https://www.gnu.org/licenses/gpl.html

The 2.0.0 version of the library has some significant changes and is not completely backwards compatible with earlier versions. These changes provide a more consistent API and reduce the possibility of name collisions. While sketches using this library will likely require changes as a result, these should be mostly straightforward.

• The library no longer defines a DS3232RTC object, therefore each sketch needs to define one. (Previous versions of the library defined a DS3232RTC object named RTC, although only for AVR architecture. Consider using a name other than RTC as this can cause a name collision on some architectures.)
• The constructor no longer has the capability to initialize the I2C bus and no longer accepts an optional parameter. Therefore, the sketch needs to call DS3232RTC::begin() in the setup() function or elsewhere as appropriate.
• To reduce the possibility of name collisions, the enumerations as well as register addresses, etc. are now defined in the header file within the DS3232RTC class. Therefore, when using any of these names, it will be necessary to include the DS3232RTC scope, e.g. myRTC.alarm(DS3232RTC::ALARM_1);
• Also to reduce collisions, register address names and bit names have been prefixed with DS32_ (see the header file.)
• The example sketches and documentation have been updated to reflect these changes.

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

The DS3232RTC library also implements functions to support the additional features of the DS3232 and DS3231. The DS3232 has the same features as the DS3231, but the DS3232 also has these extra features:

• Battery-backed SRAM
• Battery-backed 32kHz output (BB32kHz bit in Control/Status register 0x0F)
• Adjustable temperature sensor sample rate (CRATE1:0 bits in the Control/Status register).

The following example sketches are included with the DS3232RTC library:

• TimeRTC: A simple example to display the time and date.
• SetSerial: Set the RTC's date and time from the Arduino serial monitor. Displays date, time and temperature.
• rtcTimeTemp: Displays time and temperature.
• rtc_temperature: Displays time and temperature but initiates a temperature conversion every 10 seconds in addition to the RTC's default conversion period of 64 seconds.
• rtc_interrupt: Uses a 1Hz interrupt from the RTC to keep time.
• mcu_clock_drift: Demonstrates that MCU time as kept by the Time library will drift as compared to RTC time, and that MCU time may not increase by one second every second.
• tiny3232_KnockBang: Demonstrates interfacing an ATtiny45/85 to a DS3231 or DS3232 RTC.
• Several examples for using the RTC alarms. See the alarm primer for more information.

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.

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

• 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.

• 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.

Symbolic names used with alarm functions.

• ALARM_1
• ALARM_2

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

• SQWAVE_NONE
• SQWAVE_1_HZ
• SQWAVE_1024_HZ
• SQWAVE_4096_HZ
• SQWAVE_8192_HZ

Instantiates a DS3232RTC object.

DS3232RTC myRTC;

None.

None.

DS3232RTC myRTC;

Initializes the I2C bus. Calls Wire.begin().

begin();

None.

None.

DS3232RTC myRTC;
void setup() {
    myRTC.begin();
}

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.).

myRTC.get();

None.

Current date and time (time_t)

time_t myTime = myRTC.get();

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.

myRTC.set(t);

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

I2C status (uint8_t). Returns zero if successful.

// 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
myRTC.set(now());                   // set the RTC from the system time

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.

myRTC.read(tm);

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

I2C status (uint8_t). Returns zero if successful. The date and time read from the RTC are returned to the tm parameter.

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

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.

myRTC.write(tm);

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

I2C status (uint8_t). Returns zero if successful.

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

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

Set an alarm time. Sets the alarm registers only. To cause the INT pin to be asserted on alarm match, use alarmInterrupt(). This function 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.)

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

alarmType: A value from the ALARM_TYPES_t enumeration, above. (ALARM_TYPES_t)
seconds: The seconds value to set the alarm to. (uint8_t)
minutes: The minutes value to set the alarm to. (uint8_t)
hours: The hours value to set the alarm to. (uint8_t)
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. (uint8_t)

None.

// Set Alarm1 for 12:34:56 on Sunday
myRTC.setAlarm(DS3232RTC::ALM1_MATCH_DAY, 56, 34, 12, dowSunday);

Set an alarm time. Sets the alarm registers only. To cause the INT pin to be asserted on alarm match, use alarmInterrupt(). This function 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 function to set Alarm 1, the seconds value is set to zero. (Alarm 2 has no seconds register.)

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

alarmType: A value from the ALARM_TYPES_t enumeration, above. (ALARM_TYPES_t)
minutes: The minutes value to set the alarm to. (uint8_t)
hours: The hours value to set the alarm to. (uint8_t)
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. (uint8_t)

None.

// Set Alarm2 for 12:34 on the 4th day of the month
myRTC.setAlarm(DS3232RTC::ALM2_MATCH_DATE, 34, 12, 4);

Enable or disable an alarm "interrupt". Note that this "interrupt" just causes the RTC's INT pin to be asserted. To use this signal as an actual interrupt to (for example) a microcontroller, the RTC "interrupt" pin needs to be connected to the microcontroller and the microcontroller application firmware must properly configure the interrupt and also provide for handling it.

myRTC.alarmInterrupt(alarmNumber, enable);

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

None.

myRTC.alarmInterrupt(DS3232RTC::ALARM_1, true);     // assert the INT pin when Alarm1 occurs.
myRTC.alarmInterrupt(DS3232RTC::ALARM_2, false);    // disable Alarm2

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.

myRTC.alarm(alarmNumber);

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

Value of the alarm flag bit (bool)

if ( myRTC.alarm(DS3232RTC::ALARM_1) ) {		// has Alarm1 triggered?
	// yes, act on the alarm
}
else {
	// no alarm
}

Tests whether an alarm has been triggered. If the alarm was triggered, returns true, else returns false. The alarm flag is not reset.

myRTC.checkAlarm(alarmNumber);

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

Value of the alarm flag bit (bool)

if ( myRTC.checkAlarm(DS3232RTC::ALARM_1) ) {      // has Alarm1 triggered?
	// yes, act on the alarm
}
else {
	// no alarm
}

Clears the given alarm flag bit.

myRTC.clearAlarm(alarmNumber);

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

Value of the alarm flag bit, before it was cleared (bool)

if ( myRTC.checkAlarm(DS3232RTC::ALARM_1) ) {   // has Alarm1 triggered?
	myRTC.clearAlarm(DS3232RTC::ALARM_1);       // yes, clear the alarm flag
}
else {
	// no alarm
}

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.

Write one or more bytes to RTC memory.

myRTC.writeRTC(addr, values, nbytes);

addr: First SRAM address to write (uint8_t). 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 (*uint8_t)
nBytes: Number of bytes to write (uint8_t). Must be between 1 and 31 (Wire library limitation) but is not checked by the library.

I2C status (uint8_t). Returns zero if successful.

//write 1, 2, ..., 8 to the first eight DS3232 SRAM locations
uint8_t buf[8] = {1, 2, 3, 4, 5, 6, 7, 8};
myRTC.sramWrite(0x14, buf, 8);

Write a single byte to RTC memory.

myRTC.writeRTC(addr, value);

addr: SRAM address to write (uint8_t). 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 (uint8_t)

I2C status (uint8_t). Returns zero if successful.

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

Read one or more bytes from RTC RAM.

myRTC.readRTC(addr, values, nbytes);

addr: First SRAM address to read (uint8_t). 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 (*uint8_t)
nBytes: Number of bytes to read (uint8_t). Must be between 1 and 32 (Wire library limitation) but is not checked by the library.

I2C status (uint8_t). Returns zero if successful.

// read the last eight locations of SRAM into buf
uint8_t buf[8];
myRTC.sramRead(248, buf, 8);

Reads a single byte from RTC RAM.

myRTC.readRTC(addr);

addr: SRAM address to read (uint8_t). 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 read from the RTC (uint8_t)

uint8_t val;
val = myRTC.readRTC(3);  //read the value from SRAM location 3

Returns the RTC temperature.

myRTC.temperature();

None.

RTC temperature as degrees Celsius times four. (int)

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

Enables or disables the square wave output.

myRTC.squareWave(freq);

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

None.

myRTC.squareWave(DS3232RTC::SQWAVE_1_HZ);   // 1 Hz square wave
myRTC.squareWave(DS3232RTC::SQWAVE_NONE);   // no square wave

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.

myRTC.oscStopped(clearOSF);

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)

True or false (bool)

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