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RS5C372A-E2

I2C bus SERIAL INTERFACE REAL-TIME CLOCK ICs

RICOH Co.,Ltd. 

RS5C372A/B

GENERAL DESCRIPTION

1. Interfacing with the CPU

The RS5C372A/B read /write data over I2C bus interface via 2-wires: SDA (data) and SCL (clock). Since the output

of the I/O pin of SDA is open drain, data interfacing with a CPU with different supply voltage is possible by applying

pull-up resistor on the circuit board. The maximum clock frequency of 400kHz of SCL enables data transfer in I2C

bus fast mode.

2. Clock function

The clock function of the RS5C372A/B allows write/read data from lower two digits of the dominical year to sec-

onds to and from the CPU. When lower two digits of the dominical year are multiples of 4, the year is recognized as

a leap year automatically. Up to the year 2099 leap years will be automatically recognized.

*) The year 2000 is a leap year while the year 2100 is not.

3. Alarm function

˙ RS5C372A

The RS5C372A has an alarm function that outputs an interrupt signal from INTRA or INTRB output pins to the CPU

when the day of the week, hour or minute corresponds to the setting. These two systems of alarms (Alarm_A,

Alarm_B), each may output interrupt signal separately at a specified time. The alarm may be selectable between on

and off for each day of the week, thus allowing outputting alarm everyday or on a specific day of the week.

The Alarm_A is output from the INTRA pin while the Alarm_B is output from either the INTRA or the INTRB pins.

Polling is possible separately for each alarm function.

˙ RS5C372B

The RS5C372B has an alarm function that outputs an interrupt signal from INTR output pin to the CPU when the

day of the week, hour or minute corresponds to the setting. These two systems of alarms (Alarm_A, Alarm_B),

each may output interrupt signal separately at a specified time. The alarm may be selectable between on and off for

each day of the week, thus allowing outputting alarm everyday or on a specific day of the week.

Polling is possible separately for each alarm function.

4. High precision time trimming function

The RS5C372A/B have an internal oscillation circuit capacitance CG and CD so that an oscillation circuit may be con-

figured simply by externally connecting a crystal. Either 32.768kHz or 32.000kHz may be selected as a crystal oscil-

lator by setting the internal register appropriately. The RS5C372A/B incorporate a time trimming circuit that

adjusts gain or loss of the clock from the CPU up to approx. ±189ppm (±194ppm when 32.000kHz crystal is used) by

approximately 3ppm steps to correct discrepancy in oscillation frequency. (Error after correction: ±1.5ppm: 25˚C)

Thus by adjusting frequencies for each system,

· Clock display is possible at much higher precision than conventional real-time clock while using a crystal with

broader fluctuation in precision.

· Even seasonal frequency fluctuation may be corrected by adjusting seasonal clock error.

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