DS3231.py

def decimal2num(b):
    return ((b & 0xf) + 10 * (b >> 4))

def num2decimal(d):
    return (d % 10) | (d // 10) << 4

def hour_value(b):
    result = decimal2num(b & 0x1f)
    if (b & 0x20):
        result += 12
    if (b & 0x40) == 0:
        result += 8
    return result

class DS3231:
    def __init__(self, i2c, addr=0x68):
        self.i2c = i2c
        self.addr = addr

    def read_reg(self, reg, num=1):
        self.i2c.writeto(self.addr, bytearray([reg]), False)
        return self.i2c.readfrom(self.addr, num)

    def write_reg(self, reg, value):
        self.i2c.writeto(self.addr, bytearray([reg]), False)
        self.i2c.writeto(self.addr, value)

    def read(self):
        date = self.read_reg(0, 7)
        result = [2000 + decimal2num(date[6])]     # year
        result.append(decimal2num(date[5] & 0x7f)) # month
        result.append(decimal2num(date[4]))        # day
        result.append(hour_value(date[2]))         # hour
        result.append(decimal2num(date[1]))        # min
        result.append(decimal2num(date[0]))        # sec
        result.append(decimal2num(date[3]))        # day of week
        return result

    def write(self, date):
        data = [num2decimal(date[5])]
        data.append(num2decimal(date[4]))
        data.append(num2decimal(date[3]))
        data.append(date[6] & 7)
        data.append(num2decimal(date[2]))
        data.append(num2decimal(date[1]))
        data.append(num2decimal(date[0] - 2000))
        print(data)
        self.write_reg(0, bytearray(data))

    def temperature(self):
        t = self.read_reg(0x11, 2)
        return 0.25 * (t[1] >> 6) + t[0]