R2025S/D
Correction of Time Count Deviations
• The Necessity for Correction of Time Count Deviations
The oscillation frequency for R2025S/D is corrected to 0±5ppm at 25°C in fabrication. Oscillation frequency is
the fastest at 25°C, (Please see Typical Characteristics Oscillation Frequency Deviation vs. Operating temperature
(P.41)). In normal condition, temperature is not kept constant at 25°C. That is, R2025S/D loses without
correction of time counts deviation. Generally, a clock is corrected to gain 3 to 6ppm at 25°C. R2025S/D is
corrected it by setting clock adjustment register. Ricoh suggests to set 7Fh to clock adjustment register (Address
7h) for time setting to gain 3ppm at 25°C, for the equipment used indoors. And suggests to set 7Eh to clock
adjustment register (Address 7h) for time setting to gain 6ppm at 25°C, for the equipment used outdoors.
• Measurement of Oscillation Frequency
VDD
CLKC
Frequency
32KOUT
Counter
VSS
* 1) When power-on, the R2025S/D is configured to generate 32.768-kHz clock pulses for output from the
32KOUT pin.
* 2) frequency counter with 6 (more preferably 7) or more digits on the order of 1ppm is recommended for
use in the measurement of the oscillation frequency of the oscillation circuit.
• Oscillation Adjustment Circuit
The oscillation adjustment circuit can be used to correct a time count gain or loss with high precision by varying
the number of 1-second clock pulses once per 20 seconds. The oscillation adjustment circuit can be disabled by
writing the settings of "*, 0, 0, 0, 0, 0, *" ("*" representing "0" or "1") to the F6, F5, F4, F3, F2, F1, and F0 bits in the
oscillation adjustment circuit. Conversely, when such oscillation adjustment is to be made, an appropriate
oscillation adjustment value can be calculated by the equation below for writing to the oscillation adjustment circuit.
(1) When Oscillation Frequency (* 1) Is Higher Than Target Frequency (* 2) (Causing Time Count Gain)
Oscillation adjustment value (*3) = (Oscillation frequency - Target Frequency + 0.1)
Oscillation frequency × 3.051 × 10-6
≈ (Oscillation Frequency – Target Frequency) × 10 + 1
* 1) Oscillation frequency:
Frequency of clock pulse output from the 32KOUT pin at normal temperature in the manner described in "
P28 • Measurement of Oscillation Frequency".
* 2) Target frequency:
Desired frequency to be set.
Generally, a 32.768-kHz crystal oscillator has such temperature
characteristics as to have the highest oscillation frequency at normal temperature. Consequently, the crystal
oscillator is recommended to have target frequency settings on the order of 32.768 to 32.76810 kHz
(+3.05ppm relative to 32.768 kHz). Note that the target frequency differs depending on the environment or
location where the equipment incorporating the RTC is expected to be operated.
* 3) Oscillation adjustment value:
28
RICOH [ RICOH ELECTRONICS DEVICES DIVISION ]
