
2-WIRE REAL-TIME CLOCK
S-35399A03
Rev.2.0_00
Seiko Instruments Inc.
28
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)
(Minimum resolution
*4)
(Current oscillation frequency
actual measurement value
*2)
(Target oscillation frequency
*3)
×
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 when 1 Hz clock pulse is output from the
1
INT /
2
INT
pin.
*3.
Target value of average frequency when the clock correction function is used.
*4.
Refer to Table 14.
(a) Calculation example 1
In case of current oscillation frequency actual measurement value = 1.000070 [Hz], target oscillation frequency =
1.000000 [Hz], B0 = 0 (Minimum resolution = 3.052 ppm)
Correction value = 128
Integral value
()
1.000070
()
1.000000
()
1.000070
×
()
3.052
× 106
= 128
Integral value (22.93) = 128 22 = 106
Convert the correction value “106” to 7-bit binary and obtain “1101010b”.
Reverse the correction value “1101010b” and set it to B7 to B1 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)
Correction value = Integral value
(Current oscillation frequency
actual measurement value)
(Minimum resolution)
(Current oscillation frequency
actual measurement value)
(Target oscillation frequency)
×
+ 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]. B0 = 0 (Minimum resolution = 3.052 ppm)
Correction value = Integral value
()
1.000000
()
0.999920
()
0.999920
×
()
3.052
× 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], B0 = 1 (Minimum resolution = 1.017 ppm)
Correction value = Integral value
()
1.000000
()
0.999920
()
0.999920
×
()
1.017
× 10-6
+ 1
= Integral value (78.66) + 1
This calculated value exceeds the correctable range 0 to 62.
B0 = “1” (minimum resolution
= 1.017 ppm) indicates the correction is impossible.