R2025S/D
GENERAL DESCRIPTION
• Interface with CPU
The R2025S/D is connected to the CPU by two signal lines SCL and SDA, through which it reads and writes
data from and to the CPU. Since the output of the I/O pin of SDA is open drain, data interfacing with a CPU
different supply voltage is possible by applying pull-up resistors on the circuit board. The maximum clock frequency
of 400kHz (at VDD≥1.7V) of SCL enables data transfer in I2C-Bus fast mode.
• Clock and Calendar Function
The R2025S/D reads and writes time data from and to the CPU in units ranging from seconds to the last two
digits of the calendar year. The calendar year will automatically be identified as a leap year when its last two digits
are a multiple of 4. Consequently, leap years up to the year 2099 can automatically be identified as such.
• Alarm Function
The R2025S/D incorporates the alarm interrupt circuit configured to generate interrupt signals to the CPU at
preset times. The alarm interrupt circuit allows two types of alarm settings specified by the Alarm_W registers and
the Alarm_D registers. The Alarm_W registers allow week, hour, and minute alarm settings including
combinations of multiple day-of-week settings such as "Monday, Wednesday, and Friday" and "Saturday and
Sunday". The Alarm_D registers allow hour and minute alarm settings. The Alarm_W outputs from /INTRB pin,
and the Alarm_D outputs from /INTRA pin. The current /INTRA or /INTRB conditions specified by the flag bits for
each alarm function can be checked from the CPU by using a polling function.
• High-precision Oscillation Adjustment Function
To correct deviations in the oscillation frequency of the crystal oscillator, the oscillation adjustment circuit is
configured to allow correction of a time count gain or loss (up to ±1.5 ppm at 25°C) from the CPU within a
maximum range of approximately + 189 ppm in increments of approximately 3 ppm. Such oscillation frequency
adjustment in each system has the following advantages:
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Corrects seasonal frequency deviations through seasonal oscillation adjustment.
Allows timekeeping with higher precision particularly with a temperature sensing function out of RTC,
through oscillation adjustment in tune with temperature fluctuations.
• Oscillation Halt Sensing Flag, Power-on Reset Flag, and Supply Voltage Monitoring Function
The R2025S/D incorporates an oscillation halt sensing circuit equipped with internal registers configured to
record any past oscillation halt.
Power-on reset flag is set to “1” When R2025S/D is powered on from 0V.
As such, the oscillation halt sensing flag and Power-on reset flag are useful for judging the validity of time data.
The R2025S/D also incorporates a supply voltage monitoring circuit equipped with internal registers configured
to record any drop in supply voltage below a certain threshold value. Supply voltage monitoring threshold settings
can be selected between 2.1 and 1.3 volts through internal register settings. The oscillation halt sensing circuit is
configured to confirm the established invalidation of time data in contrast to the supply voltage monitoring circuit
intended to confirm the potential invalidation of time data. Further, the supply voltage monitoring circuit can be
applied to battery supply voltage monitoring.
• Periodic Interrupt Function
The R2025S/D incorporates the periodic interrupt circuit configured to generate periodic interrupt signals aside
from interrupt signals generated by the periodic interrupt circuit for output from the /INTRA pin. Periodic interrupt
signals have five selectable frequency settings of 2 Hz (once per 0.5 seconds), 1 Hz (once per 1 second), 1/60 Hz
(once per 1 minute), 1/3600 Hz (once per 1 hour), and monthly (the first day of every month). Further, periodic
interrupt signals also have two selectable waveforms, a normal pulse form (with a frequency of 2 Hz or 1 Hz) and
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RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
