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RL78/G1A CHAPTER 7 REAL-TIME CLOCK
7.4.6 Example of watch error correction of real-time clock
The watch can be corrected with high accuracy when it is slow or fast, by setting a value to the watch error correction
register.
Example of calculating the correction value
The correction value used when correcting the count value of the internal counter (16-bit) is calculated by using the
following expression.
Set the DEV bit to 0 when the correction range is −63.1 ppm or less, or 63.1 ppm or more.
(When DEV = 0)
= Number of correction counts in 1 minute ÷ 3 = (Oscillation frequency ÷ Target frequency − 1)
¯ 32768 ¯ 60 ÷ 3
Correction value
Note
(When DEV = 1)
= Number of correction counts in 1 minute = (Oscillation frequency ÷ Target frequency − 1) ¯
32768 ¯ 60
Note
Correction value
Note
The correction value is the watch error correction value calculated by using bits 6 to 0 of the watch error
correction register (SUBCUD).
(When F6 = 0) Correction value = {(F5, F4, F3, F2, F1, F0) − 1} ¯ 2
(When F6 = 1) Correction value = − {(/F5, /F4, /F3, /F2, /F1, /F0) + 1} ¯ 2
When (F6, F5, F4, F3, F2, F1, F0) is (*, 0, 0, 0, 0, 0, *), watch error correction is not performed. “*” is 0 or 1.
/F5 to /F0 are bit-inverted values (000011 when 111100).
Remarks 1. The correction value is 2, 4, 6, 8, … 120, 122, 124 or −2, −4, −6, −8, … −120, −122, −124.
2. The oscillation frequency is a value of the count clock (f
RTC).
It can be calculated from the output frequency of the RTC1HZ pin ¯ 32768 when the watch error
correction register is set to its initial value (00H).
3. The target frequency is the frequency resulting after correction performed by using the watch error
correction register.
R01UH0305EJ0200 Rev.2.00 316
Jul 04, 2013