PRELIMINARY

RV5C387A

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- 29 -

14.2.4.

Oscillation Adjustment Circuit

The oscillation adjustment circuit can be used to correct a time count gain or loss with high precision by

varying the number of 1-second clock pulses once per 20 seconds.

When such oscillation adjustment is not

to be made, the oscillation adjustment circuit can be disabled by writing the settings of "*, 0, 0, 0, 0, 0, *" ("*"

representing "0" or "1") to the F6, F5, F4, F3, F2, F1, and F0 bits in the oscillation adjustment circuit.

Conversely, when such oscillation adjustment is to be made, an appropriate oscillation adjustment value can

be calculated by the equation below for writing to the oscillation adjustment circuit.

(1) When Oscillation Frequency (* 1) Is Higher Than Target Frequency (* 2) (Causing Time Count Gain)

Oscillation adjustment value (*3) = (Oscillation frequency - Target Frequency + 0.1)

Oscillation frequency

≈ (Oscillation Frequency – Target Frequency) × 10 + 1

* 1) Oscillation frequency:

Frequency of clock pulse output from the 32KOUT pin at normal temperature in the manner described in

"14.2.2. Measurement of Oscillation Frequency".

* 2) Target frequency:

Desired frequency to be set.

Generally, a 32.768-kHz crystal oscillator has such temperature

characteristics as to have the highest oscillation frequency at normal temperature.

Consequently, the

crystal oscillator is recommended to have target frequency settings on the order of 32.768 to 32.76810 kHz

(+3.05ppm relative to 32.768 kHz).

Note that the target frequency differs depending on the environment or

location where the equipment incorporating the RTC is expected to be operated.

* 3) Oscillation adjustment value:

Value that is to be finally written to the F0 to F6 bits in the Oscillation Adjustment Register and is represented

in 7-bit coded decimal notation.

(2) When Oscillation Frequency Is Equal To Target Frequency (Causing Time Count neither Gain nor Loss)

Oscillation adjustment value = 0, +1, -64, or –63

(3) When Oscillation Frequency Is Lower Than Target Frequency (Causing Time Count Loss)

Oscillation adjustment value = (Oscillation frequency - Target Frequency)

Oscillation frequency

≈ (Oscillation Frequency – Target Frequency) × 10

Oscillation adjustment value calculations are exemplified below

(A) For an oscillation frequency = 32768.85Hz and a target frequency = 32768.05Hz

Oscillation adjustment value = (32768.85 - 32768.05 + 0.1) / (32768.85

≈ (32768.85 - 32768.05) × 10 + 1

= 9.001

≈ 9

In this instance, write the settings (F6,F5,F4,F3,F2,F1,F0)=(0,0,0,1,0,0,1) in the oscillation adjustment

register.

Thus, an appropriate oscillation adjustment value in the presence of any time count gain

represents a distance from 01h.

(B) For an oscillation frequency = 32763.95Hz and a target frequency = 32768.05Hz

Oscillation adjustment value = (32763.95 - 32768.05) / (32763.95

≈ (32763.95 - 32768.05) × 10

= -41.015

≈ -41

To represent an oscillation adjustment value of - 41 in 7-bit coded decimal notation, subtract 41 (29h)

from 128 (80h) to obtain 57h.

In this instance, write the settings of (F6,F5,F4,F3,F2,F1,F0) =

(1,0,1,0,1,1,1) in the oscillation adjustment register.

Thus, an appropriate oscillation adjustment value

in the presence of any time count loss represents a distance from 80h.

Oscillation adjustment involves an adjustment differential of approximately

±1.5ppm from the target

frequency at normal temperature.