
III PERIPHERAL MODULES 1 (SYSTEM): CLOCK MANAGEMENT UNIT (CMU)
S1C33E07 TECHNICAL MANUAL
EPSON
III-1-7
III
CMU
III.1.5 Controlling the Oscillator Circuit
III.1.5.1 OSC3 Oscillator Circuit
The OSC3 oscillator circuit generates the main clock with which to operate the C33 PE Core and internal peripheral
circuits.
Input/output pins of the OSC3 oscillator circuit
Table III.1.5.1.1 lists the input/output pins of the OSC3 oscillator circuit.
Table III.1.5.1.1 Input/Output Pins of the OSC3 Oscillator Circuit
Pin name
MCLKI
MCLKO
I/O
I
O
Function
OSC3 oscillator input pin: Crystal/ceramic oscillator or external clock input
OSC3 oscillator output pin: Crystal/ceramic oscillator (left open when using external clock input)
Structure of the oscillator circuit
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.
Oscillation circuit
control signal
SLEEP control
Oscillation circuit
control signal
SLEEP control
VSS
MCLKO
MCLKI
CD3
CG3
X'tal3
or
Ceramic
OSC3
MCLKO
MCLKI
External
clock
N.C.
VSS
VDD
OSC3
(1) Crystal/ceramic oscillation circuit
(2) External clock input
Rf
Rd
Figure III.1.5.1.1 OSC3 Oscillator Circuit
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.”
Oscillation control
CMU register control bit SOSC3 (D1/0x301B08) is used to control OSC3 oscillation.
SOSC3: High-speed Oscillation (OSC3) On/Off Control Bit in the System Clock Control Register (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
system malfunction, do not use the oscillator-derived clock until this oscillation stabilization time
elapses.