C8051F970-A-GM Datasheet, PDF (257/454 Pages) Silicon Laboratories – Low Power Capacitive Sensing MCU with up to 32 kB of Flash

C8051F97x
25.2.2. Using the SmaRTClock Oscillator in Self-Oscillate Mode
When using Self-Oscillate Mode, the XTAL3 and XTAL4 pins are internally shorted together. The following steps
show how to configure SmaRTClock for use in Self-Oscillate Mode:
1. Set SmaRTClock to Self-Oscillate Mode (XMODE = 0).
2. Set the desired oscillation frequency:
For oscillation at about 20 kHz, set BIASX2 = 0.
For oscillation at about 40 kHz, set BIASX2 = 1.
3. The oscillator starts oscillating instantaneously.
4. Fine tune the oscillation frequency by adjusting the load capacitance (RTC0XCF).
25.2.3. Using the Low Frequency Oscillator (LFO)
The low frequency oscillator provides an ultra low power, on-chip clock source to the SmaRTClock. The typical
frequency of oscillation is 16.4 kHz ±20%. No external components are required to use the LFO and the XTAL3
and XTAL4 pins do not need to be shorted together.
The following steps show how to configure SmaRTClock for use with the LFO:
1. Enable and select the Low Frequency Oscillator (LFOINT = 1).
2. The LFO starts oscillating instantaneously.
When the LFO is enabled, the SmaRTClock oscillator increments bit 1 of the 32-bit timer (instead of bit 0). This
effectively multiplies the LFO frequency by 2, making the RTC timebase behave as if a 32.768 kHz crystal is
connected at the output.
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Rev 1.0