Adafruit CircuitPython drivers for the PCF8523 realtime clock.
Latest commit 7414680 Jan 10, 2017 @tannewt tannewt Add dependencies


Introduction to Adafruit's PCF8523 Real Time Clock (RTC) Library

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This is a great battery-backed real time clock (RTC) that allows your microcontroller project to keep track of time even if it is reprogrammed, or if the power is lost. Perfect for datalogging, clock-building, time stamping, timers and alarms, etc. Equipped with PCF8523 RTC - it can run from 3.3V or 5V power & logic!

The PCF8523 is simple and inexpensive but not a high precision device. It may lose or gain up to two seconds a day. For a high-precision, temperature compensated alternative, please check out the DS3231 precision RTC. If you need a DS1307 for compatibility reasons, check out our DS1307 RTC breakout.



This driver depends on the Register and Bus Device libraries. Please ensure they are also available on the CircuitPython filesystem. This is easily achieved by downloading a library and driver bundle.

Usage Notes


Of course, you must import the library to use it:

import nativeio
import adafruit_pcf8523
import time

All the Adafruit RTC libraries take an instantiated and active I2C object (from the nativeio library) as an argument to their constructor. The way to create an I2C object depends on the board you are using. For boards with labeled SCL and SDA pins, you can:

from board import *

You can also use pins defined by the onboard microcontroller through the module.

Now, to initialize the I2C bus:

myI2C = nativeio.I2C(SCL, SDA)

Once you have created the I2C interface object, you can use it to instantiate the RTC object:

rtc = adafruit_pcf8523.PCF8523(myI2C)

Date and time

To set the time, you need to set datetime to a time.struct_time object:

rtc.datetime = time.struct_time((2017,1,9,15,6,0,0,9,-1))

After the RTC is set, you retrieve the time by reading the datetime attribute and access the standard attributes of a struct_time such as tm_year, tm_hour and tm_min.

t = rtc.datetime
print(t.tm_hour, t.tm_min)


To set the time, you need to set alarm to a tuple with a time.struct_time object and string representing the frequency such as "hourly":

rtc.alarm = (time.struct_time((2017,1,9,15,6,0,0,9,-1)), "daily")

After the RTC is set, you retrieve the alarm status by reading the alarm_status attribute. Once True, set it back to False to reset.

if rtc.alarm_status:
    print("wake up!")
    rtc.alarm_status = False

API Reference