General description
The PCF2127A is a CMOS1 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 PCF2127A has 512 bytes of general purpose static RAM, a selectable I2C-bus or SPI-bus, a backup battery switch-over circuit, a programmable watchdog function, a timestamp function, and many other features.

Features and benefits
■ Temperature Compensated Crystal Oscillator (TCXO) with integrated capacitors
■ Typical accuracy: ±3 ppm from −15 °C to +60 °C
■ Integration of a 32.768 kHz quartz crystal and oscillator in the same package
■ Provides year, month, day, weekday, hours, minutes, and seconds
■ 512 bytes of general purpose static RAM
■ Timestamp function
    ◆ with interrupt capability
    ◆ detection of two different events on one multilevel input pin (e.g. for tamper detection)
■ Two line bidirectional 400 kHz Fast-mode I2C-bus interface (IOL = 3 mA at pin SDA/CE)
■ 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 pin
■ Battery low detection function
■ Extra power fail detection function with input and output pins
■ Power-On Reset Override (PORO)
■ Oscillator stop detection function
■ Interrupt output and system reset pin (open-drain)
■ Programmable 1 second or 1 minute interrupt
■ Programmable countdown timer with interrupt capability
■ Programmable watchdog timer with interrupt and reset capability
■ Programmable alarm function with interrupt capability
■ Programmable square wave open-drain output pin
■ Clock operating voltage: 1.2 V to 4.2 V
■ Low supply current: typical 0.65 μA at VDD = 3.0 V and Tamb = 25 °C
■ Automatic leap year correction

Applications
■ Electronic metering for electricity, water, and gas
■ Timekeeping instruments with high precision
■ GPS equipment to reduce time to first fix
■ Applications that require an accurate process timing
■ Products with long automated unattended operation time