
iiiPeriPheraLModuLes1(systeM):CLoCkManageMentunit(CMu)
iii-1-8
ePson
s1C33L17teChniCaLManuaL
iii.1.5.2settingtheosC3divider
An OSC3 divided clock can be used as the system clock when OSC3 is selected as the system clock source. Setting
the system clock to the lowest frequency possible according to the processing can reduce current consumption.
The OSC3 divider generates six kinds of clocks from OSC31/1 to OSC31/32. Select a divided clock from those
six clocks using OSC3DIV[2:0] (D[10:8]/0x301B08).
osC3diV[2:0]:OSC3ClockDividerSelectBitsintheSystemClockControlRegister(D[10:8]/0x301B08)
TableIII.1.5.2.1SelectinganOSC3DividedClock
osC3diV2
1
0
osC3diV1
1
0
1
0
osC3_diV
OSC31/1
OSC31/32
OSC31/16
OSC31/8
OSC31/4
OSC31/2
OSC31/1
osC3diV0
1
0
1
0
1
0
1
0
(Default:0b000=OSC31/1)
A divided clock can be selected at any time. However, up to 32 OSC3 clock cycles are required before the clocks
are actually changed after altering the register values.
iii.1.5.3osC1oscillatorCircuit
The S1C33L17 contains an oscillator circuit (OSC1) used to generate a 32.768 kHz (typ.) clock as the clock source
for timekeeping operation of the RTC.
The OSC1 clock can also be used as a power-saving operating clock for the core system or peripheral circuits.
input/outputpinsoftheosC1oscillatorcircuit
Table III.1.5.3.1 lists the input/output pins of the OSC1 oscillator circuit.
TableIII.1.5.3.1Input/OutputPinsoftheLow-speed(OSC1)OscillatorCircuit
Pinname
RTC_CLKI
RTC_CLKO
i/o
I
O
Function
OSC1inputpin:Crystaloscillatororexternalclockinput
OSC1outputpin:Crystaloscillatoroutput(leftopenwhenexternalclockisinput)
structureoftheosC1oscillatorcircuit
The OSC1 oscillator circuit accommodates a crystal oscillator and external clock input. The core voltage VDD
supplies power for this circuit. Figure III.1.5.3.1 shows the structure of the OSC1 oscillator circuit.
Lowlevel
Oscillationcircuit
controlsignal
Oscillationcircuit
controlsignal
OSC1
RTC_CLKO
RTC_CLKI
External
clock
N.C.
VSS
VDD
OSC1
(1)Crystaloscillationcircuit
VSS
RTC_CLKO
RTC_CLKI
Oscillationcircuit
controlsignal
(3)Whennotused
(2)Externalclockinput
VSS
RTC_CLKO
RTC_CLKI
CD1
CG1
X'tal1
Rf
Rd
FigureIII.1.5.3.1OSC1OscillatorCircuit