The PCF2129 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 very low power consumption. The PCF2129 has a selectable I²C-bus or SPI-bus, a backup battery switch-over circuit, a programmable watchdog function, a timestamp function, and many other features.
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## Features
* Operating temperature range from -40 °C to +85 °C
* Temperature Compensated Crystal Oscillator (TCXO) with integrated capacitors
* Typical accuracy:
* PCF2129AT: ±3 ppm from -15 °C to +60 °C
* PCF2129T: ±3 ppm from -30 °C to +80 °C
* Integration of a 32.768 kHz quartz crystal and oscillator in the same package
* Provides year, month, day, weekday, hours, minutes, seconds, and leap year correction
* Timestamp function:
* with interrupt capability
* detection of two different events on one multilevel input pin (for example, for tamper detection)
* Two line bidirectional 400 kHz Fast-mode I²C-bus interface
* 3 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 Override (PORO)
* Oscillator stop detection function
* Interrupt output (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: 1.8 V to 4.2 V
* Low supply current: typical 0.70 μA at VDD = 3.3 V
## Target 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
