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S-35392A Datasheet, PDF (25/47 Pages) Seiko Instruments Inc – 2-WIRE REAL-TIME CLOCK | |||
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Rev.1.3_00
2-WIRE REAL-TIME CLOCK
S-35392A
1. How to calculate
(1) If current oscillation frequency > target frequency (in case the clock is fast)
Correction value*1 = 128 â Integral value
(Current oscillation frequency
actual measurement value*2)
â
(Target oscillation frequency*3)
(Current oscillation frequency
actual measurement value*2)
Ã
(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 â(a) Calculation
example 1â.
*2. Measurement value when 1 Hz clock pulse is output from the INT2 pin.
*3. Target value of average frequency when the clock correction function is used.
*4. Refer to Table 12.
(a) Calculation example 1
In case of current oscillation frequency actual measurement value = 1.000070 [Hz], target oscillation frequency =
1.000000 [Hz], B7 = 0 (Minimum resolution = 3.052 ppm)
Correction
value =
128 â
Integral value

ï£
(1.000070) â (1.000000)
(1.000070) Ã (3.052 Ã 10â6)


= 128 â Integral value (22.93)= 128 â 22 = 106
Convert the correction value â106â to 7-bit binary and obtain â1101010bâ.
Reverse the correction value â1101010bâ 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) = (0, 1, 0, 1, 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) â actual measurement value)
(Current oscillation frequency
actual measurement value)
Ã
(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 = 0.999920 [Hz], target oscillation frequency =
1.000000 [Hz]. B7 = 0 (Minimum resolution = 3.052 ppm)
Correction
value =
Integral
value

ï£
(1.000000) â (0.999920)
(0.999920) Ã (3.052 Ã 10-6)


+1
= Integral value (26.21) + 1 = 26 + 1 = 27
Thus, set the clock correction register:
(B7, B6, B5, B4, B3, B2, B1, B0) = (1, 1, 0, 1, 1, 0, 0, 0)
(b) Calculation example 3
In case of current oscillation frequency actual measurement value = 0.999920 [Hz], target oscillation frequency =
1.000000 [Hz], B7 = 1 (Minimum resolution = 1.017 ppm)
Correction
value =
Integral
value

ï£
(1.000000) â (0.999920)
(0.999920) Ã (1.017 Ã 10-6)


+1
= Integral value (78.66) + 1
Thus, this calculated value exceeds the correctable range 0 to 62,
B7 = â1â (minimum resolution = 1.017 ppm) indicates the correction is impossible.
Seiko Instruments Inc.
25
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