DS3231M is the real time clock (RTC) used on the MAXREFDES130. The key feature of this RTC is the MEMS resonator. For a cost-effective RTC, the MEMS resonator provides ruggedness and better accuracy at 5 ppm over a longer period of time compared to a crystal integrated into the chip. It uses a low 200 µA supply current. Due to the popularity of the DS3231M, many lines of open source firmware are publicly available for use in both Arduino and mbed development environments.