The PCA8802 is a CMOS integrated circuit for battery operation, typically supplied by
button cells or flexible polymer batteries. Incorporated is a 32.768 kHz quartz crystal
oscillator circuit including the two load capacitors. The circuit is optimized for a quartz with
6 pF load capacitance specification. Higher values can also be used with the addition of
external load capacitors.
The main function of the oscillator is to generate a 1⁄32 Hz clock signal which is used to
increment a 24 bit binary counter. The counter can be read over the serial interface and
can also be set to any desired value. Control over the divider chain also allows for
accurate starting of the counter. Incrementing of the counter value during read is
prevented by freezing of the counter during access.
An interrupt signal is also available and is triggered coincident with the counter updating.
This signal can be used as a wake-up for a microcontroller.