Smartcard RTC; ultra low power oscillator with integrated counter for initiating one time password generation

The PCF8802 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.