S-35192A Datasheet, PDF (23/41 Pages) Seiko Instruments Inc – 3-WIRE REAL-TIME CLOCK

Rev.1.2_00
3-WIRE REAL-TIME CLOCK
S-35192A
1. How to calculate
(1) If current oscillation frequency > target frequency (in case the clock is fast)
Correction value^*1 = 128 − Integral value
(Current oscillation frequency
actual measurement value^*2)
−
(Target oscillation frequency^*3)
(Current oscillation frequency
actual measurement value^*2)
×
(Minimum resolution^*4)
Caution The figure range which can be corrected is that the calculated value is from 0 to 64.
*1. Convert this value to be set in the clock correction register. For how to convert, refer to “(a) Calculation
example 1”.
*2. Measurement value of a clock pulse output from the 32KO pin.
*3. Target value of average frequency when the clock correction function is used.
*4. Refer to Table 11.
(a) Calculation example 1
In case of current oscillation frequency actual measurement value = 32.771 [kHz], target oscillation frequency =
32.768 [kHz], B7 = 0 (Minimum resolution = 3.052 ppm)
Correction
value =
128 −
Integral value


(32771) − (32768)
(32771) × (3.052 × 10^−6)


= 128 − Integral value (29.99)= 128 − 29 = 99
Convert the correction value “99” to 7-bit binary and obtain “01100011 b”.
Reverse the correction value “01100011 b” and set it to B6 to B0 of the clock correction register.
Thus, set the clock correction register:
(B7, B6, B5, B4, B3, B2, B1, B0) = (1, 1, 0, 0, 0, 1, 1, 0)
(2) If current oscillation frequency < target frequency (in case the clock is slow)
(Current oscillation frequency
Correction value = Integral value
(Target oscillation frequency) − _{actual measurement value)}
(Current oscillation frequency
actual measurement value)
×
(Minimum resolution)
+1
Caution The figure range which can be corrected is that the calculated value is from 0 to 62.
(a) Calculation example 2
In case of current oscillation frequency actual measurement value = 32.765 [kHz], target oscillation frequency =
32.768 [kHz]. B7 = 0 (Minimum resolution = 3.052 ppm)
Correction value =
Integral value


(32768) − (32765)
(32765) × (3.052 × 10^-6)


+1
= Integral value (30.00) + 1 = 30 + 1 = 31
Thus, set the clock correction register:
(B7, B6, B5, B4, B3, B2, B1, B0) = (1, 1, 1, 1, 1, 0, 0, 0)
(b) Calculation example 3
In case of current oscillation frequency actual measurement value = 32.765 [kHz], target oscillation frequency =
32.768 [kHz], B7 = 1 (Minimum resolution = 1.017 ppm)
Correction value =
Integral value


(32768) − (32765)
(32765) × (1.017 × 10^-6)


+1
= Integral value (90.03) + 1
Thus, this calculated value exceeds the correctable range 0 to 62,
B7 = “1” (minimum resolution = 1.017 ppm) indicates the correction is impossible.
Seiko Instruments Inc.
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