S35390A datasheet(27/51 Pages) SII

27 / 51 page

FOR AUTOMOTIVE 105°C OPERATION 2-WIRE REAL-TIME CLOCK

Rev.2.2_00

S-35390A H Series

Seiko Instruments Inc.

1. How to calculate

1. 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 "(1) Calculation

example 1".

*2.

Measurement value when 1 Hz clock pulse is output from the

INT

pin (or

INT

pin).

*3.

Target value of average frequency when the function of clock correction is used.

*4.

Refer to "Table 14 Function of Clock Correction".

(1) 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

× 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 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)

1. 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.

(1) 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)

(2) 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.

S35390A Datasheet(PDF) 27 Page - Seiko Instruments Inc

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