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UM10503
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User manual
Rev. 2.1 — 10 December 2015
1100 of 1441
NXP Semiconductors
UM10503
Chapter 37: LPC43xx/LPC43Sxx Real-Time Clock (RTC)
•
The SEC timer and the calibration counter count up for every 1 Hz clock cycle.
•
When the calibration counter reaches CALVAL, a calibration match occurs and all
RTC timers will be stopped for one clock cycle so that the timers will not increment in
the next cycle.
•
If an alarm match event occurs in the same cycle as the calibration match, the alarm
interrupt will be delayed by one cycle to avoid a double alarm interrupt.
Forward calibration
Enable the RTC timer and calibration in the CCR register (set bits CLKEN = 1 and
CCALEN = 0). In the CALIBRATION register, set the calibration value CALVAL
1 and
select CALDIR = 0.
•
The SEC timer and the calibration counter count up for every 1 Hz clock cycle.
•
When the calibration counter reaches CALVAL, a calibration match occurs and the
RTC timers are incremented by 2.
•
When the calibration event occurs, the LSB of the ALSEC register is forced to be one
so that the alarm interrupt will not be missed when skipping a second.