Library: DS3231 - Rinky-Dink Electronics

This library has been made to easily interface and use the DS3231 RTC with an Arduino or chipKit. The library will also work with the DS3232 RTC chip but you will not be able to use the internal SRAM.

The DS3231 is a low-cost, extremely accurate I2C realtime clock (RTC) with an integrated temperature-compensated crystal oscillator (TCXO) and crystal. The device incorporates a battery input, and maintains accurate timekeeping when main power to the device is interrupted. The integration of the crystal resonator enhances the long-term accuracy of the device as well as reduces the piece-part count in a manufacturing line. The DS3231 is available in commercial and industrial temperature ranges, and is offered in a 16-pin, 300-mil SO package.

The RTC maintains seconds, minutes, hours, day, date, month, and year information. The date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. The clock operates in either the 24-hour or 12-hour format with an AM/PM indicator. Two programmable time-of-day alarms and a programmable square-wave output are provided. Address and data are transferred serially through an I2C bidirectional bus.

A precision temperature-compensated voltage reference and comparator circuit monitors the status of VCC to detect power failures, to provide a reset output, and to automatically switch to the backup supply when necessary. Additionally, the RST pin is monitored as a pushbutton input for generating a μP reset.

Please note that this library only makes use of the 24-hour format, and that alarms are not implemented.

The library has not been tested in combination with the Wire library and I have no idea if they can share pins. Do not send me any questions about this. If you experience problems with pin-sharing you can move the DS3231/DS3232 SDA and SCL pins to any available pins on your development board. This library will in this case fall back to a software-based, TWI-/I2C-like protocol which will require exclusive access to the pins used.

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Nice to know:

This library will default to I2C Fast Mode (400 KHz) when using the hardware I2C interface.

I highly recommend using the DS3231 (or DS3232) instead of the DS1307. While the DS3231/DS3232 may be slightly more expensive than the DS1307 it is much more accurate due to the internal TCXO (temperature-compensated crystal oscillator) and crystal. This also means that you don’t have to use an external crystal like you have to with the DS1307.

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