Datasheet

78K0/Kx2-L CHAPTER 10 REAL-TIME COUNTER
R01UH0028EJ0400 Rev.4.00 394
Sep 27, 2010
Correction example <1>
Example of correcting from 32772.3 Hz to 32768 Hz (32772.3 Hz − 131.2 ppm)
[Measuring the oscillation frequency]
The oscillation frequency
Note
of each product is measured by outputting about 32 kHz from the RTCCL pin or
outputting about 1 Hz from the RTC1HZ pin when the watch error correction register is set to its initial value (00H).
Note Refer to 10.4.5 1 Hz output of real-time counter for the setting procedure of outputting about 1 Hz from the
RTC1HZ pin, and 10.4.6 32.768 kHz output of real-time counter for the setting procedure of outputting about
32 kHz from the RTCCL pin.
[Calculating the correction value]
(When the output frequency from the RTCCL pin is 32772.3 Hz)
If the target frequency is assumed to be 32768 Hz (32772.3 Hz − 131.2 ppm), the correction range for −131.2 ppm is
−63.1 ppm or less, so assume DEV to be 0.
The expression for calculating the correction value when DEV is 0 is applied.
Correction value = Number of correction counts in 1 minute ÷ 3
= (Oscillation frequency ÷ Target frequency − 1) ¯ 32768 ¯ 60 ÷ 3
= (32772.3 ÷ 32768 − 1) ¯ 32768 ¯ 60 ÷ 3
= 86
[Calculating the values to be set to (F6 to F0)]
(When the correction value is 86)
If the correction value is 0 or more (when delaying), assume F6 to be 0.
Calculate (F5, F4, F3, F2, F1, F0) from the correction value.
{ (F5, F4, F3, F2, F1, F0) − 1} ¯ 2 = 86
(F5, F4, F3, F2, F1, F0) = 44
(F5, F4, F3, F2, F1, F0) = (1, 0, 1, 1, 0, 0)
Consequently, when correcting from 32772.3 Hz to 32768 Hz (32772.3 Hz − 131.2 ppm), setting the correction
register such that DEV is 0 and the correction value is 86 (bits 6 to 0 of SUBCUD: 0101100) results in 32768 Hz (0
ppm).
Figure 10-27 shows the operation when (DEV, F6, F5, F4, F3, F2, F1, F0) is (0, 0, 1, 0, 1, 1, 0, 0).