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41.3.2 Time counter
The time counter consists of a 32-bit seconds counter that increments once every second
and a 16-bit prescaler register that increments once every 32.768 kHz clock cycle. There
is also the option to clock the prescaler using a 1 kHz LPO that increments the prescaler
by 32 on every clock cycle.
Reading the time counter (either seconds or prescaler) while it is incrementing may return
invalid data due to synchronization of the read data bus. If it is necessary for software to
read the prescaler or seconds counter when they could be incrementing, it is
recommended that two read accesses are performed and that software verifies that the
same data was returned for both reads.
The time seconds register and time prescaler register can be written only when SR[TCE]
is clear. Always write to the prescaler register before writing to the seconds register,
because the seconds register increments on the falling edge of bit 14 of the prescaler
register.
The time prescaler register increments provided SR[TCE] is set, SR[TIF] is clear,
SR[TOF] is clear, and the 32.768 kHz (or 1 kHz) clock source is present. After enabling
the oscillator, wait the oscillator startup time before setting SR[TCE] to allow time for
the oscillator clock output to stabilize.
If the time seconds register overflows then the SR[TOF] will set and the time prescaler
register will stop incrementing. Clear SR[TOF] by initializing the time seconds register.
The time seconds register and time prescaler register read as zero whenever SR[TOF] is
set.
SR[TIF] is set on POR and software reset and is cleared by initializing the time seconds
register. The time seconds register and time prescaler register read as zero whenever
SR[TIF] is set.
41.3.3 Compensation
The compensation logic provides an accurate and wide compensation range and can
correct errors as high as 3906 ppm and as low as 0.12 ppm. The compensation factor
must be calculated externally to the RTC and supplied by software to the compensation
register. The RTC itself does not calculate the amount of compensation that is required,
although the 1 Hz clock is output to an external pin in support of external calibration
logic.
Functional description
K32 L2A Reference Manual, Rev. 2, 01/2020
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NXP Semiconductors
Содержание K32 L2A Series
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