General description
The PCF2131 is a CMOS Real Time Clock (RTC) and calendar with an integrated
Temperature Compensated Crystal (Xtal) Oscillator (TCXO) and a 32.768 kHz quartz
crystal optimized for very high accuracy and ultra low power consumption. The
PCF2131 has a selectable I2C-bus or SPI-bus, a backup battery switch-over circuit, a
programmable watchdog function, four timestamps function, and many other features.

Features and benefits
• Operating temperature range from -40 °C to +85 °C
• Temperature Compensated Crystal Oscillator (TCXO) with trimmed integrated
capacitors
• Ultra low supply current: typical 64 nA at VDD = 3.3 V
• Temperature compensated RTC, typical accuracy ±3 ppm from -40 °C to +85 °C
• Integration of a 32.768 kHz quartz crystal and oscillator in the same package
• Provides year, month, day, weekday, hours, minutes, seconds and 1/100 seconds
• Provides leap year correction
• Timestamp function
– with interrupt capability
– detection of four different events on four input pins (for example, for tamper detection)
• 2-line bidirectional 400 kHz Fast-mode I2C-bus interface
• 4-line SPI-bus with separate data input and output (maximum speed 6.5 Mbit/s)
• Battery backup input pin and switch-over circuitry
• Battery backed output voltage
• Battery low detection function
• Power-On Reset (POR)
• Power-On Reset Override (PORO) function
• Software reset function
• Two interrupt outputs (open-drain)
• Programmable 1 second or 1 minute interrupt
• Programmable watchdog timer with interrupt
• Programmable alarm function with interrupt capability
• Programmable square output
• Clock operating voltage: 1.2 V to 5.5 V

Applications
• Electronic metering for electricity, water, and gas
• Precision timekeeping
• Access to accurate time of the day
• GPS equipment to reduce time to first fix
• Applications that require an accurate process timing
• Products with long automated unattended operation time