General description

The PCF2128 is a ready to run CMOS real time clock/calendar with an integrated temperature compensated crystal oscillator (TCXO). In timekeeping applications the high accuracy of the PCF2128 allows it to be used as a replacement for costly and higher powered long wave receivers or GPS receivers. A programmable battery switch-over circuit enables an uninterruptible power supply and consequently continuous timekeeping. The PCF2128 additionally features 512 bytes of general purpose RAM, a programmable watchdog, a time stamp facility and a voltage monitoring facility. Programming is possible using either an SPI or an I2C-bus interface.

■ Integration of a 32.768 kHz quartz crystal in the same package as the RTC

■ temperature compensated crystal oscillator (TCXO) with integrated capacitors.

■ accuracy:

typically 3 ppm from−20 °C to +70 °C,

typically 5 ppm from −40 °C to +85 °C

■ provides year, month, day, weekday, hours, minutes and seconds

■ programmable alarm function with interrupt capability

■ programmable countdown timer with interrupt capability

■ programmable watchdog timer with interrupt and reset capability

■ timestamp function with interrupt capability

■ battery backup input pin and switch-over circuitry

■ extra power fail detection with input and output pins

■ battery low detection

■ battery backed output voltage pin

■ 512 bytes of general purpose static RAM

■ 1 second or 1 minute interrupt output

■ oscillator stop detection

■ two line bi-directional 1 MHz fast mode plus I2C interface

■ timestamp input

■ power-on reset

■ 3 line SPI interface with separate data input and output (maximum speed 6.5 Mbits/s)

■ programmable square wave output pin

■ I2C-bus slave address: read A3H and write A2H

■ clock operating voltage: to 5.5 V

■ low backup current; typical 0.95 μA at VDD = 3.0 V and Tamb = 25 °C

■ selectable I2C and SPI interface