The Real Time Counter has several operation modes. The main mode is Calendar Timer Mode which automatically counts years, months, weeks, days, hours, minutes and seconds up to 99 years based on the 32kHz sub-oscillator input signal. This counter allows the micro to be in sleep mode for several days before the core needs to be woken up. During this time the real-time operation continues in the system. An additional mode is Constant Period Interrupt mode, where in addition to the calendar timer functionality, the timer is able to generate an interrupt with a fixed period from half a second to one month. An alarm interrupt function is also implemented, which allows one to set up an alarm value to wake up the micro at a specific date - selectable by week, hour and minute. And finally a 1Hz pin output function is included to generate a very slow 1Hz signal on an output pin.