RS5C372B(1997) View Datasheet(PDF) - RICOH Co.,Ltd.

Part Name

Description

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RS5C372B
(Rev.:1997)

I2C-bus Serial Interface Real Time Clock (8pin SSOP)

RICOH Co.,Ltd. 

RS5C372B

s Outline Description

1. Interfacing with the CPU

The RS5C372B reads/writes data over I2C-bus interface via two signal lines: 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 resistance on the circuit board. The maximum clock frequency of

400kHz of SCL enables data transfer in I2C-bus high-speed mode.

2. Clock function

The clock function of the RS5C372B allows write/read data from lower two digits of the dominical year to

seconds 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

The RS5C372B has an alarm function that outputs an interrupt signal from /INTR 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 and ALARM_B is output from the /INTR pins. Polling is possible separately for each alarm

system.

4. High precision time trimming function

The RS5C372B has internal oscillation circuit capacitance CG and CD so that an oscillation circuit may be

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

crystal oscillator by setting the internal register appropriately. The RS5C372B incorporates 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.

• For those systems that have temperature detection precision of clock function may be increased by

correcting clock error according to temperature fluctuations.

5. Oscillation halt sensing

The oscillation halt sensing function uses a register to store oscillation halt information. This function may

be used to determine if the RS5C372B supply power has been booted from 0V and if it has been backed up.

This function is useful for deter-mining if clock data is valid or invalid.

6. Periodic interrupt

The RS5C372B can output periodic interrupt pulses in addition to alarm function from the /INTR pin. This

frequency may be selected from 2Hz (every 0.5 seconds), 1Hz (every second), 1/60Hz (every minute),

1/3600Hz (every hour) and monthly (1st of month).

Output wave form for periodic interrupt may be selected from regular pulse wave form (2Hz and 1Hz) and

wave forms (every second, every minute, every hour and every month) that are appropriate for CPU level

interrupt. The RS5C372B has polling function that monitors pin status in the register.

7. 32kHz clock output

The RS5C372B may output oscillation frequency from the 32KOUT pin. This clock output is set for output by

default, which is set to on or off by setting the register. This pin functions as an CMOS push-pull output.

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