R×5C338A
2.2 Measurement of Oscillation Frequency
R×5C338A
VDD
OSCIN
OSCOUT
CLKC
32KOUT
VSS
32.768kHz
Frequency
counter
*1) The R×5C338A are configured to generate 32.768-kHz clock pulses for output from the 32KOUT pin at power-on conditionally on setting the XSTP bit
to 1 in the control register 2.
*2) A 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 fre-
quency of the oscillation circuit.
*3) The CLKC input should be connected to the VDD pin with a pull-up resistor.
2.3 Adjustment of Oscillation Frequency
The oscillation frequency of the oscillation circuit can be adjusted by varying procedures depending on the usage of
the R×5C338A in the system into which they are to be built and on the allowable degree of time count errors. The
flow chart below serves as a guide to selecting an optimum oscillation frequency adjustment procedure for the
relevant system.
Start
Use 32-kHz NO
clock circuit?
YES
Allowable time count precision is on order of oscillation
frequency variations of crystal oscillator *1 plus
frequency variations of real-time clock? *2, *3
YES
Use 32-kHz clock circuit without regard
to its frequency precision?
NO
Allowable time count precision is on order of oscillation
frequency variations of crystal oscillator *1 plus
frequency variations of real-time clock? *2, *3
YES
NO
YES
NO
To Course (A)
To Course (B)
To Course (C)
To Course (D)
*1) Generally, crystal oscillators for commercial use are classified in terms of their center frequency depending on their load capacitance (CL) and further
divided into ranks on the order of ±10, ± 20, and ±50 ppm depending on the degree of their oscillation frequency variations.
*2) Basically, the R×5C338A are configured to cause frequency variations on the order of ±5 to ±10ppm at normal temperature.
*3) Time count precision as referred to in the above flow chart is applicable to normal temperature and actually affected by the temperature characteristics
and other properties of crystal oscillators.
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