3-WIRE REAL-TIME CLOCK
S-35190A
Rev.2.4_00
1. How to calculate
(1) If current oscillation frequency > target frequency (in case the clock is fast)
(Current oscillation frequency
(Target oscillation frequency*3)
actual measurement value*2)
−
Correction value*1 = 128 − Integral value
(Current oscillation frequency
(Minimum resolution*4)
×
actual measurement value*2)
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 INT 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)
1.000070
− 1.000000
( )
(
)
Correction value = 128 − Integral value
6
1.000070
×
3.052 × 10−
(
)
(
)
= 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 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
actual measurement value)
−
(Target oscillation frequency)
+ 1
Correction value = Integral value
(Current oscillation frequency
actual measurement value)
×
(Minimum resolution)
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)
1.000000
− 0.999920
( )
(
)
Correction value = Integral value
+ 1
0.999920
(
×
3.052 × 10-6
(
)
)
= 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)
1.000000
− 0.999920
( )
(
)
Correction value = Integral value
+ 1
0.999920
×
1.017 × 10-6
(
)
(
)
= Integral value (78.66) + 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.
27
SII [ SEIKO INSTRUMENTS INC ]
