DATASHEET: 
PCF8563-04.pdf
General description
The PCF8563 is a CMOS real time clock/calendar optimized for low power consumption. A programmable clock output, interrupt output and voltage-low detector are also provided. All address and data are transferred serially via a two-line bidirectional I2C-bus. Maximum bus speed is 400 kbit/s. The built-in word address register is incremented automatically after each written or read data byte.
Features
Provides year, month, day, weekday, hours, minutes and seconds based on 32.768 kHz quartz crystal
Century flag
Clock operating voltage: 1.8 V to 5.5 V
Low backup current; typical 0.25 uA at VDD = 3.0 V and Tamb = 25 Cel.
400 kHz two-wire I2C-bus interface (at VDD = 1.8 V to 5.5 V)
Programmable clock output for peripheral devices (32.768 kHz, 1024 Hz, 32 Hz and 1 Hz)
Alarm and timer functions
Integrated oscillator capacitor
Internal power-on reset
I2C-bus slave address: read A3H and write A2H
Open-drain interrupt pin.
Applications
Mobile telephones
Portable instruments
Fax machines
Battery powered products.
