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RL78/G1A CHAPTER 7 REAL-TIME CLOCK
Correction example 2
Example of correcting from 32767.4 Hz to 32768 Hz (32767.4 Hz + 18.3 ppm)
[Measuring the oscillation frequency]
Note
The oscillation frequency
of each product is measured by outputting about 1 Hz from the RTC1HZ pin when the
watch error correction register (SUBCUD) is set to its initial value (00H).
Note
See 7.4.5 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
= (Oscillation frequency ÷ Target frequency − 1) ¯ 32768 ¯ 60
= (32767.4 ÷ 32768 − 1) ¯ 32768 ¯ 60
= −36
[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 = −36
(/F5, /F4, /F3, /F2, /F1, /F0) = 17
(/F5, /F4, /F3, /F2, /F1, /F0) = (0, 1, 0, 0, 0, 1)
(F5, F4, F3, F2, F1, F0) = (1, 0, 1, 1, 1, 0)
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 7-26 shows the operation when (DEV, F6, F5, F4, F3, F2, F1, F0) is (1, 1, 1, 0, 1, 1, 1, 0).
R01UH0305EJ0200 Rev.2.00 319
Jul 04, 2013