During chip power-down, RTC is powered from the backup power supply (VBAT) and iselectrically isolated from the rest of the chip but continues to increment the time counter(if enabled) and retain the state of the RTC registers. The RTC registers are notaccessible.During chip power-up, RTC remains powered from the backup power supply (VBAT).All RTC registers are accessible by software and all functions are operational. If enabled,the 32.768 kHz clock can be supplied to the rest of the chip.42.1.3 RTC signal descriptionsTable 42-1. RTC signal descriptionsSignal Description I/OEXTAL32 32.768 kHz oscillator input IXTAL32 32.768 kHz oscillator output ORTC_CLKOUT 1 Hz square-wave output or OSCERCLK ORTC_WAKEUP Wakeup for external device O42.1.3.1 RTC clock outputThe clock to the seconds counter is available on the RTC_CLKOUT signal. It is a 1 Hzsquare wave output. See RTC_CLKOUT options for details.42.1.3.2 RTC wakeup pinThe RTC wakeup pin is an open drain, active low, output that allows the RTC to wakeupthe chip via an external component. The wakeup pin asserts when the wakeup pin enableis set and either the RTC interrupt is asserted or the wakeup pin is turned on via a registerbit. The wakeup pin does not assert from the RTC seconds interrupt.NOTEThe wakeup pin is optional and may not be implemented on alldevices.IntroductionK22F Sub-Family Reference Manual, Rev. 4, 08/20161052 NXP Semiconductors
