406
/
838
Nations Technologies Inc.
Tel
:
+86-755-86309900
:
Address: Nations Tower, #109 Baoshen Road, Hi-tech Park North.
Nanshan District, Shenzhen, 518057, P.R.China
f
CAL
=
𝑓
𝑅𝑇𝐶𝐶𝐿𝐾
∗ (1 +
256−𝑅𝑇𝐶_𝐶𝐴𝐿𝐼𝐵.𝐶𝑀[8:0]
2
20
+ 𝑅𝑇𝐶_𝐶𝐴𝐿𝐼𝐵.𝐶𝑀[8:0]– 265
)
Verify RTC calibration
RTC output 1Hz waveform for measuring and verifying RTC precision.
Up to 2 RTCCLK cycles measurement error may occur when measure the RTC frequency in a limit measurement
period. If the measurement period is the same as calibration period, the error can be eliminated.
The calibration period is 32 seconds (default).
Using an accurate 32-second period to measure the 1Hz calibration output can ensure that the measurement error
is within 0.447ppm (0.5 RTCCLK cycles within 32 seconds).
The calibration period is 16 seconds.
Using an accurate 16-second period to measure the 1Hz calibration output can ensure that the measurement error
is within 0.954ppm (0.5 RTCCLK cycles within 16 seconds).
The calibration period is 8 seconds.
Using an accurate 8-second period to measure the 1Hz calibration output can ensure that the measurement error
is within 1.907ppm (0.5 RTCCLK cycles within 8 seconds).
Dynamic recalibration
When RTC_INITSTS.INITF=0, RTC_CALIB register can update by using following steps:
Wait RTC_INITSTS.RECPF=0.
A new value is written to the RTC_CALIB, then RTC_INITSTS.RECPF is automatically set to 1.
The new calibration settings will take effect within 3 ck_apre cycles after a data write to the RTC_CALIB.
14.2.18
RTC low power mode
The working state of RTC in low power mode.
Lower Power Mode
RTC Working State
Exit Low Power Mode
SLEEP
Normal work
RTC interrupt
STOP0
Normal work when the clock source of RTC is LSE
or LSI
Alarm A, Alarm B, Periodic Wakeup, Tamper
event and Timestamp event
STOP2
Normal work when the clock source of RTC is
LSE or LSI
Alarm A, Alarm B, Periodic Wakeup, Tamper
event and Timestamp event
STANDBY
Normal work when the clock source of RTC is LSE
or LSI
Alarm A, Alarm B, Periodic Wakeup, Tamper
event and Timestamp event