Updates to the time compensation register will not take effect until the next time the time
seconds register increments and provided the previous compensation interval has expired.
When the compensation interval is set to other than once a second then the compensation
is applied in the first second interval and the remaining second intervals receive no
compensation.
Compensation is disabled by configuring the time compensation register to zero.
When the prescaler is configured to increment using the 1 kHz LPO, the effective
compensation value is divided by 32 and can only adjust the number of clock cycles
between -4 and +3.
43.4.4 Time alarm
The Time Alarm register (TAR), SR[TAF], and IER[TAIE] allow the RTC to generate an
interrupt at a predefined time. The 32-bit TAR is compared with the 32-bit Time Seconds
register (TSR) each time it increments. SR[TAF] will set when TAR equals TSR and
TSR increments.
SR[TAF] is cleared by writing TAR. This will usually be the next alarm value, although
writing a value that is less than TSR, such as 0, will prevent SR[TAF] from setting again.
SR[TAF] cannot otherwise be disabled, although the interrupt it generates is enabled or
disabled by IER[TAIE].
43.4.5 Update mode
The Update Mode field in the Control register (CR[UM]) configures software write
access to the Time Counter Enable (SR[TCE]) field. When CR[UM] is clear, SR[TCE]
can be written only when LR[SRL] is set. When CR[UM] is set, SR[TCE] can also be
written when SR[TCE] is clear or when SR[TIF] or SR[TOF] are set. This allows the
time seconds and prescaler registers to be initialized whenever time is invalidated, while
preventing the time seconds and prescaler registers from being changed on the fly. When
LR[SRL] is set, CR[UM] has no effect on SR[TCE].
43.4.6 Register lock
The Lock register (LR) can be used to block write accesses to certain registers until the
next POR or software reset. Locking the Control register (CR) will disable the software
reset. Locking LR will block future updates to LR.
Chapter 43 Real Time Clock (SRTC)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors
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