CP2400 SILABS [Silicon Laboratories], CP2400 Datasheet - Page 74

• Manufacturer Part Number: CP2400
• Description: 128/64 SEGMENT LCD DRIVER
• Manufacturer: SILABS [Silicon Laboratories]

CP2400/1/2/3
11.2. SmaRTClock Clocking Sources
The SmaRTClock peripheral is clocked from its own timebase, independent of the system clock. The SmaRTClock
timebase is derived from the SmaRTClock oscillator circuit, which has two modes of operation: crystal mode, and
self-oscillate mode. The oscillation frequency is 32.768 kHz in crystal mode and can be programmed in the range
of sub 20 kHz to above 40 kHz in self-oscillate mode. In crystal mode, XTAL1 and XTAL2 may be overdriven by an
external CMOS clock.
11.2.1. Using the SmaRTClock Oscillator with a Crystal or External CMOS Clock
When using crystal mode, a 32.768 kHz crystal should be connected between XTAL3 and XTAL4. No other
external components are required. The following steps show how to start the SmaRTClock crystal oscillator in
software:
1. Set SmaRTClock to Crystal Mode (XMODE = 1).
2. Optional. Enable/Disable Automatic Gain Control (AGCEN) and Bias Doubling (BIASX2). See Section 11.2.4 for
3. Set the desired loading capacitance (RTC0XCF).
4. Enable power to the SmaRTClock oscillator circuit (RTC0EN = 1).
5. Wait 2 ms.
6. Poll the SmaRTClock Clock Valid Bit (CLKVLD) until the crystal oscillator stabilizes.
7. Poll the SmaRTClock Load Capacitance Ready Bit (LOADRDY) until the load capacitance reaches its
8. Enable the SmaRTClock missing clock detector.
9. Wait 2 ms.
10.Clear the PMU0CF wake-up source flags.
In crystal mode, the SmaRTClock oscillator may be driven by an external CMOS clock. The CMOS clock should be
applied to both XTAL1 and XTAL2. The input low voltage (VIL) and input high voltage (VIH) for these pins when
used with an external CMOS clock are 0.1 and 0.8 V, respectively. The SmaRTClock oscillator should be
configured to its lowest bias setting with AGC disabled. The CLKVLD bit is indeterminate when using a CMOS
clock, however, the OSCFAIL bit may be checked 2 ms after SmaRTClock oscillator is powered on to ensure that
there is a valid clock.
11.2.2. Using the SmaRTClock Oscillator in Self-Oscillate Mode
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:
3. The oscillator starts oscillating instantaneously.
4. Fine tune the oscillation frequency by adjusting the load capacitance (RTC0XCF).
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recommendations on using these oscillator features.
programmed value.
For oscillation at about 20 kHz, set BIASX2 = 0.
For oscillation at about 40 kHz, set BIASX2 = 1.
Rev. 1.0