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RV5C387A Datasheet(PDF) 33 Page - RICOH electronics devices division |
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RV5C387A Datasheet(HTML) 33 Page - RICOH electronics devices division |
33 / 49 page ![]() 33 RV5C387A Course (A) When the time count precision of each real-time clock is not to be adjusted, the crystal oscillator intended for use with that real-time clock may have any CL value requiring no presetting. The crystal oscillator may be subject to frequency variations which are selectable within the allowable range of time count precision. Several crystal oscillators and real-time clocks should be used to find the center frequency of the crystal oscillators by the method described in “2.2 Measurement of Oscillation Frequency” and then calculate an appropriate oscillation adjustment value by the method described in “2.4 Oscillation Adjustment Circuit” for writing this value to the RV5C387A. Course (B) When the time count precision of each real-time clock is to be adjusted within the oscillation frequency variations of the crystal oscillator plus the frequency variations of the real-time clock ICs, it becomes necessary to correct deviations in the time count of each real-time clock by the method described in “2.4 Oscillation Adjustment Circuit”. Such oscillation adjustment provides crystal oscillators with a wider range of allowable settings of their oscillation frequency variations and their CL values. The real-time clock IC and the crystal oscillator intended for use with that real-time clock IC should be used to find the center frequency of the crystal oscillator by the method described in “2.2 Measurement of Oscillation Frequency” and then confirm the center frequency thus found to fall within the range adjustable by the oscillation adjustment circuit before adjusting the oscillation frequency of the oscillation circuit. At normal temperature, the oscillation frequency of the oscillator circuit can be adjusted by up to approximately ±1.5ppm. Course (C) Course (C) together with Course (D) requires adjusting the time count precision of each real-time clock as well as the frequency of 32.768-kHz clock pulses output from the 32KOUT pin. Normally, the oscillation frequency of the crystal oscillator intended for use with the real-time clocks should be adjusted by adjusting the oscillation stabilizing capacitors CG and CD connected to both ends of the crystal oscillator. The RV5C387A, which incorporates the CG and the CD, require adjusting the oscillation frequency of the crystal oscillator through its CL value. Generally, the relationship between the CL value and the CG and CD values can be represented by the following equation: CL = CG × CD + CS where “CS” represents the floating capacity of the printed circuit board CG + CD The crystal oscillator intended for use with the RV5C387A is recommended to have the CL value on the order of 6 to 8pF. Its oscillation frequency should be measured by the method described in “2.2 Measurement of Oscillation Frequency”. Any crystal oscillator found to have an excessively high or low oscillation frequency (causing a time count gain or loss, respectively) should be replaced with another one having a smaller and greater CL value, respectively until another one having an optimum CL value is selected. In this case, the bit settings disabling the oscillation adjustment circuit (see “2.4 Oscillation Adjustment Circuit”) should be written to the oscillation adjustment register. |
Similar Part No. - RV5C387A_03 |
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Similar Description - RV5C387A_03 |
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