UPD78F1502AGK-GAK-AX Datasheet, PDF (388/1031 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcontrollers

78K0R/Lx3
CHAPTER 7 REAL-TIME COUNTER
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^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 See 7.4.5 1 Hz output of real-time counter for the setting procedure of outputting about 1 Hz from the RTC1HZ
pin, and 7.4.6 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 RTC1Hz 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 speeding up), 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)
= −36
= 17
= (0, 1, 0, 0, 0, 1)
= (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 SUBCUD: 1101110) results in 32768 Hz (0
ppm).
Figure 7-28 shows the operation when (DEV, F6, F5, F4, F3, F2, F1, F0) is (1, 1, 1, 0, 1, 1, 1, 0).
R01UH0004EJ0501 Rev.5.01
372
Jun 20, 2011