RTC_IER field descriptions (continued)Field Description0 Seconds interrupt is disabled.1 Seconds interrupt is enabled.3ReservedThis field is reserved.2TAIETime Alarm Interrupt Enable0 Time alarm flag does not generate an interrupt.1 Time alarm flag does generate an interrupt.1TOIETime Overflow Interrupt Enable0 Time overflow flag does not generate an interrupt.1 Time overflow flag does generate an interrupt.0TIIETime Invalid Interrupt Enable0 Time invalid flag does not generate an interrupt.1 Time invalid flag does generate an interrupt.34.3 Functional description34.3.1 Power, clocking, and resetThe 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 anexternal crystal using the oscillator.The power-on-reset signal initializes all RTC registers to their default state. A softwarereset bit can also initialize all RTC registers.34.3.1.1 Oscillator controlThe 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 settingSR[TCE] or using the oscillator clock external to the RTC.The crystal oscillator includes tunable capacitors that can be configured by software. Donot change the capacitance unless the oscillator is disabled.Functional descriptionKL25 Sub-Family Reference Manual, Rev. 3, September 2012606 Freescale Semiconductor, Inc.
