NXP Semiconductors K22F series, Reference Manual, Page: 1052 / 1407

During chip power-down, RTC is powered from the backup power supply (VBAT) and is
electrically 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 not
accessible.
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 descriptions
Table 42-1. RTC signal descriptions
Signal Description I/O
EXTAL32 32.768 kHz oscillator input I
XTAL32 32.768 kHz oscillator output O
RTC_CLKOUT 1 Hz square-wave output or OSCERCLK O
RTC_WAKEUP Wakeup for external device O
42.1.3.1 RTC clock output
The clock to the seconds counter is available on the RTC_CLKOUT signal. It is a 1 Hz
square wave output. See
RTC_CLKOUT options for details.
42.1.3.2 RTC wakeup pin
The RTC wakeup pin is an open drain, active low, output that allows the RTC to wakeup
the chip via an external component. The wakeup pin asserts when the wakeup pin enable
is set and either the RTC interrupt is asserted or the wakeup pin is turned on via a register
bit. The wakeup pin does not assert from the RTC seconds interrupt.
NOTE
The wakeup pin is optional and may not be implemented on all
devices.
Introduction
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
1052 NXP Semiconductors