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RS5C338A-E2

3-WIRE SERIAL INTERFACE REAL-TIME CLOCK ICS WITH VOLTAGE MONITORING FUNCTION

RICOH Co.,Ltd. 

R×5C338A

Another advisable way to select a crystal oscillator having an optimum CL value is to contact the manufacturer of the

crystal oscillator intended for use with the R×5C338A.

Incidentally, the high oscillation frequency of the crystal oscillator can also be adjusted by adding an external

oscillation stabilization capacitor CGOUT as illustrated in the diagram below.

R× 5C338A

VDD

10

VDD

*1) The CGOUT should have a capacitance ranging from 0 to 15pF.

RF

CG

RD CD

OSCIN

9

32kHz

CGOUT *1

8

OSCOUT

Course (D)

It is necessary to select the crystal oscillator in the same manner as in Course (C) as well as correct errors in the

time count of each real-time clock in the same manner as in Course (B) by the method described in “2.4 Oscillation

Adjustment Circuit”.

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.

2.4-1 When Oscillation Frequency *1 is Higher than Target Frequency *2 (There is a Time Count Gain)

(Oscillation frequency – Target frequency + 0.1)

Oscillation adjustment value*3 =

Oscillation frequency × 3.051 × 10–6

.= (Oscillation frequency – Target frequency) × 10 + 1

*1) Oscillation frequency:

Frequency of clock pulses output from the 32KOUT pin at normal temperature in the manner described in “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 32.76810kHz (+3.05ppm relative to 32.768kHz). Note that the target

frequency differs depending on the environment or location where the equipment incorporating the real-time clocks 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.

30

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