R
×
5C348A/B
GENERAL DESCRIPTION
1. Interface with CPU
The R
×
5C348A/B are connected to the CPU by four signal lines CE (Chip Enable), SCLK (Serial Clock), SI (Serial
Input), and SO (Serial Output), through which they read and write data from and to the CPU. The CPU can access
when the CE pin is held high. Access clock pulses have a maximum frequency of 2MHz (at 5 volts), allowing high-
speed data transfer to the CPU.
2. Clock and Calendar Function
The R
×
5C348A/B read and write 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. Also available is the 1900/2000 identification bit for Year 2000 compliance. 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.
3. Alarm Function
The R
×
5C348A/B incorporate an alarm circuit configured to generate interrupt signals to the CPU for output from
the INTR pin at preset times. The alarm 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 current alarm settings specified by
these two registers can be checked from the CPU by using a polling function.
4. High-precision Oscillation Adjustment Function
The R
×
5C348A/B have built-in oscillation stabilization capacitors (C
G
and C
D
), which can be connected to an
external crystal oscillator to configure an oscillation circuit. 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 ±1.5ppm at 25˚C) from the CPU within a maximum range of 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 real-time clocks while using a crysta
l oscillator with a wide range of precision variations.
·
Corrects seasonal frequency deviations through seasonal oscillation adjustment.
·
Allows timekeeping with higher precision particularly in systems with a temperature sensing function
through oscillation adjustment in tune with temperature fluctuations.
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RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
