NXP Semiconductors K32 L2A Series, Reference Manual, Page: 1051 / 1379

41.3 Functional description
41.3.1 Power, clocking, and reset
The RTC is an always powered block that remains active in all low power modes.
The time counter within the RTC is clocked by a 32.768 kHz clock sourced from an
external crystal using the oscillator. Alternatively, the time counter can be clocked by the
LPO and the prescaler will increment by 32 for each LPO clock.
The power-on-reset signal initializes all RTC registers to their default state. A software
reset bit can also initialize all RTC registers.
41.3.1.1 Oscillator control
The 32.768 kHz crystal oscillator is disabled at POR and must be enabled by software.
After enabling the cystal oscillator, wait the oscillator startup time before setting
SR[TCE] or using the oscillator clock external to the RTC.
The crystal oscillator includes tunable capacitors that can be configured by software. Do
not change the capacitance unless the oscillator is disabled.
41.3.1.2 Software reset
Writing 1 to CR[SWR] forces the equivalent of a POR to the rest of the RTC module.
CR[SWR] is not affected by the software reset and must be cleared by software.
41.3.1.3 Supervisor access
When the supervisor access control bit is clear, only supervisor mode software can write
to the RTC registers, non-supervisor mode software will generate a bus error. Both
supervisor and non-supervisor mode software can always read the RTC registers.
Chapter 41 Real Time Clock (RTC)
K32 L2A Reference Manual, Rev. 2, 01/2020
NXP Semiconductors 1051