The NXP PCF8523 is a CMOS1 real time clock and calendar optimized for low power consumption. Data is transferred serially via the I2C bus with a maximum data rate of 1000 kbit/s. Alarm and timer functions are available with the possibility to generate a wake up signal on an interrupt pin. An offset register allows fine tuning of the clock.

Open-drain interrupt or clock output pins
Programmable offset register for frequency adjustment