The PCF8523 is a CMOS Real-Time Clock (RTC) and calendar optimized for low power consumption. It uses the I2C interface for data communication. Timer and alarm functionality is available to generate wake-up signals on an interrupt pin. Fine-tuning of the clock is possible due to the presence of an offset register. The PCF8523 has a backup battery switch-over circuit, which detects power failures and automatically switches to the battery supply when a power failure occurs.