The PCF8563 is a CMOS real-time clock (RTC) and calendar that is best suited for low-power applications. Programmable clock outputs, interrupt outputs, and undervoltage detectors are also available. All addresses and data are transmitted serially over a two-wire bidirectional I2C bus. The maximum bus speed is 400 kbit\/s. The register address is incremented automatically after each data byte is written or read. .