Windows 10 IoT Core DS3231

RPi GPIO

Name	Board Pin
32K	N/A
SQW	N/A
SCL	5
SDA	3
VCC	1/17
GND	6/9/14/20/25/30/34/39

using System;
using Windows.Devices.I2c;

namespace CYFang
{
    /// <summary>
    /// RS3231 RTC
    /// </summary>
    public class DS3231 : IDisposable
    {
        /// <summary>
        /// Slave address
        /// </summary>
        private const int SLAVE_ADDRESS = 0x68;

        /// <summary>
        /// I2C
        /// </summary>
        private I2cDevice device;

        /// <summary>
        /// DS3231
        /// </summary>
        public DS3231()
        {
            InitI2C();
        }

        /// <summary>
        /// Init I2C
        /// </summary>
        private async void InitI2C()
        {
            var settings = new I2cConnectionSettings(SLAVE_ADDRESS);
            var controller = await I2cController.GetDefaultAsync();
            device = controller.GetDevice(settings);
        }

        /// <summary>
        /// Set date and time to DS3231
        /// </summary>
        /// <param name="dt"></param>
        public void SetDateTimeToDS3231(DateTime dt)
        {
            byte write_seconds = DecToBcd(dt.Second);
            byte write_minutes = DecToBcd(dt.Minute);
            byte write_hours = DecToBcd(dt.Hour);
            byte write_dayofweek = DecToBcd((int)dt.DayOfWeek);
            byte write_day = DecToBcd(dt.Day);
            byte write_month = DecToBcd(dt.Month);
            byte write_year = DecToBcd(dt.Year % 100);

            byte[] write_time = { 0x00, write_seconds, write_minutes, write_hours, write_dayofweek, write_day, write_month, write_year };
            device.Write(write_time);
        }

        /// <summary>
        /// Get date and time from DS3231
        /// </summary>
        /// <returns></returns>
        public DateTime GetDateTimeFromDS3231()
        {
            byte[] writeBuff = { 0x00 };
            device.Write(writeBuff);

            byte[] readBuff = new byte[7];
            device.Read(readBuff);

            int second = BcdToDec((byte)(readBuff[0] & 0x7f));
            int minute = BcdToDec(readBuff[1]);
            int hour = BcdToDec((byte)(readBuff[2] & 0x3f));
            int dayOfWeek = BcdToDec(readBuff[3]);
            int dayOfMonth = BcdToDec(readBuff[4]);
            int month = BcdToDec(readBuff[5]);
            int year = BcdToDec(readBuff[6]) + 2000;

            return new DateTime(year, month, dayOfMonth, hour, minute, second);
        }

        /// <summary>
        /// Binary-Coded Decimal
        /// </summary>
        /// <param name="val"></param>
        /// <returns></returns>
        private static byte DecToBcd(int val) { return (byte)((val / 10 * 16) + (val % 10)); }

        /// <summary>
        /// Binary-Coded Decimal
        /// </summary>
        /// <param name="val"></param>
        /// <returns></returns>
        private static int BcdToDec(int val) { return ((val / 16 * 10) + (val % 16)); }

        /// <summary>
        /// Dispose
        /// </summary>
        public void Dispose()
        {
            if (device != null)
            {
                device.Dispose();
                device = null;
            }
        }
    }
}

參考資料：
https://datasheets.maximintegrated.com/en/ds/DS3231.pdf