General description
The PCF2123 is a CMOS1 Real-Time Clock (RTC) and calendar optimized for low power applications. Data is transferred serially via a Serial Peripheral Interface (SPI-bus) with a maximum data rate of 6.25 Mbit/s. An alarm and timer function is also available providing the possibility to generate a wake-up signal on an interrupt pin. An offset register allows fine tuning of the clock.

Features and benefits
■ Real time clock provides year, month, day, weekday, hours, minutes, and seconds based on a 32.768 kHz quartz crystal
■ Low backup current while running: typical 100 nA at VDD = 2.0 V and Tamb = 25 °C
■ Resolution: seconds to years
■ Watchdog functionality
■ Freely programmable timer and alarm with interrupt capability
■ Clock operating voltage: 1.1 V to 5.5 V
■ 3 line SPI-bus with separate, but combinable data input and output
■ Serial interface at VDD = 1.8 V to 5.5 V
■ 1 second or 1 minute interrupt output
■ Integrated oscillator load capacitors for CL = 7 pF
■ Internal Power-On Reset (POR)
■ Open-drain interrupt and clock output pins
■ Programmable offset register for frequency adjustment

Applications
■ Time keeping application
■ Battery powered devices
■ Metering
■ High duration timers
■ Daily alarms
■ Low standby power applications