Rx5C348A/B
GENERAL DESCRIPTION
Interface with CPU
The Rx5C348A/B is connected to the CPU by four signal lines CE (Chip Enable), SCLK (Serial Clock), SI (Serial
Input), and SO (Serial Output), through which it reads and writes data from and to the CPU. The CPU can be
accessed when the CE pin is held high. Access clock pulses have a maximum frequency of 1 MHz allowing
high-speed data transfer to the CPU.
Clock and Calendar Function
The Rx5C348A/B 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.
*) The year 2000 is a leap year while the year 2100 is not a leap year.
Alarm Function
The Rx5C348A/B 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 /INTR pin, and
the Alarm_D outputs also from /INTR pin. Each alarm function can be checked from the CPU by using a polling
function.
High-precision Oscillation Adjustment Function
The Rx5C348A/B has built-in oscillation stabilization capacitors (CG and CD), which can be connected to an
external crystal oscillator to configure an oscillation circuit. To correct deviations in the oscillator frequency of
the crystal, the oscillation adjustment circuit is configured to allow correction of a time count gain or loss (up to
±1.5ppm
at 25°C) from the CPU. The maximum range is approximately
±189ppm
in increments of approximately
3ppm. Such oscillation frequency adjustment in each system has the following advantages:
* Allows timekeeping with much higher precision than conventional RTCs while using a crystal oscillator
with a wide range of precision variations.
* 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.
Power-on Reset, Oscillation Halt Sensing Function and Supply Voltage Monitoring Function
The Rx5C348A/B incorporates an oscillation halt sensing circuit equipped with internal registers configured to
record any past oscillation halt.
Power on reset function reset the control resisters when the system is powered on from 0V. At the same time, the
fact is memorized to the resister as a flag, thereby identifying whether they are powered on from 0V or battery
backed-up.
The Rx5C348A/B 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 2.1V and 1.6V through internal register settings. The sampling rate is
normally 1s.
The oscillation halt sensing circuit and the power-on reset flag are 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 Rx5C348A/B incorporates the periodic interrupt circuit configured to generate periodic interrupt signals
aside from interrupt signals generated by the alarm interrupt circuit for output from the /INTR 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 special form adapted to interruption from the CPU in the level mode (with second, minute, hour,
and month interrupts). The condition of periodic interrupt signals can be monitored with using a polling function.
32kHz Clock Output
The Rx5C348A/B incorporates a 32-kHz clock circuit configured to generate clock pulses with the oscillation
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Rev.2.01
-9-
RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
