Renesas RL78 Series User Manual page 311

RL78/G1D
Correction example 2
Example of correcting from 32767.4 Hz to 32768 Hz (32767.4 Hz + 18.3 ppm)
[Measuring the oscillation frequency]
The oscillation frequency
watch error correction register (SUBCUD) is set to its initial value (00H).
Note See 8.4.5 1 Hz output of real-time clock for the setting procedure of outputting about 1 Hz from the RTC1HZ
pin.
[Calculating the correction value]
(When the output frequency from the RTCCL pin is 0.9999817 Hz)
Oscillation frequency = 32768 × 0.9999817 ≈ 32767.4 Hz
Assume the target frequency to be 32768 Hz (32767.4 Hz + 18.3 ppm) and DEV to be 1.
The expression for calculating the correction value when DEV is 1 is applied.
Correction value = Number of correction counts in 1 minute
[Calculating the values to be set to (F6 to F0)]
(When the correction value is –36)
If the correction value is 0 or less (when quickening), assume F6 to be 1.
Calculate (F5, F4, F3, F2, F1, F0) from the correction value.
– {(/F5, /F4, /F3, /F2, /F1, /F0) – 1} × 2
(/F5, /F4, /F3, /F2, /F1, /F0)
(/F5, /F4, /F3, /F2, /F1, /F0)
(F5, F4, F3, F2, F1, F0)
Consequently, when correcting from 32767.4 Hz to 32768 Hz (32767.4 Hz + 18.3 ppm), setting the correction
register such that DEV is 1 and the correction value is –36 (bits 6 to 0 of the SUBCUD register: 1101110) results in
32768 Hz (0 ppm).
Figure 8-26 shows the operation when (DEV, F6, F5, F4, F3, F2, F1, F0) is (1, 1, 1, 0, 1, 1, 1, 0).
R01UH0515EJ0120 Rev.1.20
Dec 16, 2016
Note
of each product is measured by outputting about 1 Hz from the RTC1HZ pin when the
= (Oscillation frequency ÷ Target frequency – 1) × 32768 × 60
= (32767.4 ÷ 32768 – 1) × 32768 × 60
= –36
CHAPTER 8 REAL-TIME CLOCK
= –36
= 17
= (0, 1, 0, 0, 0, 1)
= (1, 0, 1, 1, 1, 0)
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