SiM3C1xx
4.3.1. PLL (PLL0)
The PLL module consists of a dedicated Digitally-Controlled Oscillator (DCO) that can be used in Free-Running
mode without a reference frequency, Frequency-Locked to a reference frequency, or Phase-Locked to a reference
frequency. The reference frequency for Frequency-Lock and Phase-Lock modes can use one of multiple sources
(including the external oscillator) to provide maximum flexibility for different application needs. Because the PLL
module generates its own clock, the DCO can be locked to a particular reference frequency and then moved to
Free-Running mode to reduce system power and noise.
The PLL module includes the following features:
Five
output ranges with output frequencies ranging from 23 to 80 MHz.
Multiple reference frequency inputs.
Three output modes: free-running DCO, frequency-locked, and phase-locked.
Ability to sense the rising edge or falling edge of the reference source.
DCO frequency LSB dithering to provide finer average output frequencies.
Spectrum spreading to reduce generated system noise.
Low jitter and fast lock times.
Ability to suspend all output frequency updates (including dithering and spectrum spreading) using the
STALL bit during jitter-sensitive operations.
4.3.2. Low Power Oscillator (LPOSC0)
The Low Power Oscillator is the default AHB oscillator on SiM3C1xx devices and enables or disables
automatically, as needed.
The Low Power Oscillator has the following features:
20
MHz and divided 2.5 MHz frequencies available for the AHB clock.
Automatically starts and stops as needed.
4.3.3. Low Frequency Oscillator (LFOSC0)
The low frequency oscillator (LFOSC0) provides a low power internal clock source running at approximately
16.4 kHz for the RTC0 timer and other peripherals on the device. No external components are required to use the
low frequency oscillator
4.3.4. External Oscillators (EXTOSC0)
The EXTOSC0 external oscillator circuit may drive an external crystal, ceramic resonator, capacitor, or RC
network. A CMOS clock may also provide a clock input. The external oscillator output may be selected as the AHB
clock or used to clock other modules independent of the AHB clock selection.
The External Oscillator control has the following features:
Support
for external crystal, RC, C, or CMOS oscillators.
Support external CMOS frequencies from 10 kHz to 50 MHz and external crystal frequencies from 10 kHz
to 30 MHz.
Various drive strengths for flexible crystal oscillator support.
Internal frequency divide-by-two option available.
38
Preliminary Rev. 0.8
SILABS [ SILICON LABORATORIES ]
