Product Highlights: Two time-of-day alarms.Programmable square-wave output signal.RST output/pushbutton reset debounce input.Battery-backup input for continuous timekeeping.Simple serial interface connects to most microcontrollers. Pin Description: 32KHz：32KHz outputSQW：Active LOW Interrupt or Square wave outputSCL：Serial Clock InputSDA：Serial Data I/OVCC：DC Power Pin GND：Ground The DS3231 is a low-cost, extremely accurate, I2C real time clock (RTC). The clock operates in either the 24-hour or 12-hour format with an AM/PM indicator.Clock chip: high-precision clock chip DS3231. (there are 3 different chips for this clock module: DS3231N, DS3231SN and DS3231M, we send it by randomly.) Wiring instructions (for example compatible with Arduino uno r3 ): SCL → A5SDA → A4VCC → 5VGND → GND Package Included: 3 X DS3231 Clock module Module Parameters: 1. Size: 38mm (L) * 22mm (W) * 14mm (H) 2. Weight: 8g 3. Operating voltage: 3.3-5.5V 4. Clock chip: high-precision clock chip DS3231. (there are 3 different chips for this clock module: DS3231N, DS3231SN and DS3231M, we send it by randomly) 5. Clock Accuracy: 0-40 ℃ range, the accuracy 2ppm, the error was about 1 minute 6. Memory chips: AT24C32 (storage capacity 32K) 7. Real time clock generator seconds, minutes, hours, day, date, month and year. And provide valid until the year 2100 leap year compensation 8. Chip temperature sensor comes with an accuracy of ± 3 ℃ 9. IIC bus interface, the maximum transmission speed of 400KHz (working voltage of 5V) 10. Can be cascaded with other IIC device, 24C32 addresses can be shorted A0/A1/A2 modify default address is 0x57