
iiiPeriPheraLModuLes1(systeM):CLoCkManageMentunit(CMu)
s1C33L17teChniCaLManuaL
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iii-1-7
III
CMU
iii.1.5ControllingtheoscillatorCircuit
iii.1.5.1osC3oscillatorCircuit
The OSC3 oscillator circuit generates the main clock with which to operate the C33 PE Core and internal peripheral
circuits.
input/outputpinsoftheosC3oscillatorcircuit
Table III.1.5.1.1 lists the input/output pins of the OSC3 oscillator circuit.
TableIII.1.5.1.1Input/OutputPinsoftheOSC3OscillatorCircuit
Pinname
MCLKI
MCLKO
i/o
I
O
Function
OSC3oscillatorinputpin:Crystal/ceramicoscillatororexternalclockinput
OSC3oscillatoroutputpin:Crystal/ceramicoscillator(leftopenwhenusingexternalclockinput)
structureoftheoscillatorcircuit
The OSC3 oscillator circuit accommodates a crystal/ceramic oscillator and external clock input. The core
voltage VDD supplies power for this circuit.
Figure III.1.5.1.1 shows the structure of the OSC3 oscillator circuit.
Oscillationcircuit
controlsignal
SLEEPcontrol
Oscillationcircuit
controlsignal
SLEEPcontrol
VSS
MCLKO
MCLKI
CD3
CG3
X'tal3
or
Ceramic
OSC3
MCLKO
MCLKI
External
clock
N.C.
VSS
VDD
OSC3
(1)Crystal/ceramicoscillationcircuit
(2)Externalclockinput
Rf
Rd
FigureIII.1.5.1.1OSC3OscillatorCircuit
For use as a crystal or ceramic oscillator circuit, connect a crystal (X’tal3) or ceramic resonator and a feedback
resistor (Rf), two capacitors (CG3, CD3) and, if necessary, a drain resistor (Rd) to the MCLKI and MCLKO pins
and VSS.
To use an external clock, leave the MCLKO pin open and input a VDD-level clock (with a 50% duty cycle) to
the MCLKI pin.
The range of oscillation frequencies is as follows:
Crystal oscillator:
5 MHz (min.) to 48 MHz (max.)
Ceramic oscillator:
5 MHz (min.) to 48 MHz (max.)
External clock input:
5 MHz (min.) to 48 MHz (max.)
A 48 MHz clock source with 0.25% of accuracy should be connected for using the USB function.
Before using a ceramic resonator, please be sure to contact Murata Manufacturing Co., Ltd. for further
information on conditions of use for ceramic resonators.
For details of oscillation characteristics and external clock input characteristics, see “Electrical Characteristics.”
oscillationcontrol
CMU register control bit SOSC3 (D1/0x301B08) is used to control OSC3 oscillation.
sosC3:High-speedOscillation(OSC3)On/OffControlBitintheSystemClockControlRegister(D1/0x301B08)
Setting this control bit to 0 causes the OSC3 oscillator circuit to stop; setting it to 1 causes the OSC3 oscillator
circuit to start oscillating, thereby outputting a clock signal waveform. When initially reset, this bit is set to 1
for enabling OSC3 oscillation.
note: When the oscillator is made to start oscillating by setting SOSC3 (D1/0x301B08) from 0 to 1,
a finite time is required until oscillation stabilizes (see“Electrical Characteristics”).To prevent
systemmalfunction,donotusetheoscillator-derivedclockuntilthisoscillationstabilizationtime
elapses.