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To abort reference oscillation or sensor oscillation, write 0 to the RFC_nTRG.SREF bit (reference
oscillation), the RFC_nTRG.SSENA bit (sensor A oscillation), or the RFC_nTRG.SSENB bit (sensor B
oscillation) used to start the oscillation. The counters maintain the value at the point they stopped,
note, however, that the conversion results cannot be guaranteed if the oscillation is resumed. When
resuming oscillation, execute from counter initialization again.
Conversion error
Performing reference oscillation and sensor oscillation with the same resistor and capacitor results
n ≈ m. The difference between n and m is a conversion error. Table 20.4.4.1 lists the error factors.
(n: measurement counter initial value, m: measurement counter value at the end of sensor
oscillation)
20.4.5. CR Oscillation Frequency Monitoring Function
The CR oscillation clock (RFCLK) generated during converting operation can be output from the
RFCLKOn pin for monitoring. By setting the RFC_nCTL.CONEN bit to 1, the RFC Ch.n enters continuous
oscillation mode that disables oscillation stop conditions to continue oscillating operations. In this case,
set the RFC_nTRG.SREF bit (reference oscillation), the RFC_nTRG.SSENA bit (sensor A oscillation), or the
RFC_nTRG.SSENB bit (sensor B oscillation) to 1 to start oscillation. Set the bit to 0 to stop oscillation.
Using this function helps easily measure the CR oscillation clock frequency. Furthermore, setting the
RFC_nCTL.RFCLKMD bit to 1 changes the output clock to the divided-by-two RFCLK clock.
RFC_nTRG.SSENA, SSENB, SREF
(RFC_nCTL.RFCLKMD = 0)
(RFC_nCTL.RFCLKMD = 1)
S1C31D50 TECHNICAL MANUAL
(Rev. 1.00)
Table 20.4.4.1 Error Factors
Error factor
External part tolerances
Power supply voltage fluctuations
Parasitic capacitance and resistance of the board
Temperature
Unevenness of IC quality
Writing 1
RFC_nCTL.CONEN
RFINn pin
RFCLKOn pin
RFCLKOn pin
Figure 20.4.5.1 CR Oscillation Clock (RFCLK) Waveform
Seiko Epson Corporation
Influence
Large
Large
Middle
Small
Small
Writing 0
V
DD
V
SS
V
DD
V
SS
20-7
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