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2.3.3. Clock Sources
IOSC oscillator circuit
The IOSC oscillator circuit features a fast startup and no external parts are required for oscillating.
Figure 2.3.3.1 shows the configuration of the IOSC oscillator circuit.
The IOSC oscillator circuit output clock IOSCCLK is used as SYSCLK at booting. The IOSCCLK
frequency can be selected using the CLGIOSC.IOSCFQ[1:0] bits. For more information for the
oscillation characteristics, refer to "IOSC oscillator circuit characteristics" in the "Electrical
Characteristics" chapter, respectively.
OSC1 oscillator circuit
The OSC1 oscillator circuit is a low-power oscillator circuit that allows software to select the
oscillator type from two different types shown below. Figure 2.3.3.2 shows the configuration of the
OSC1 oscillator circuit.
OSC1 oscillator circuit
Selector
External gate
capacitor C
G1
OSC1
OSC2
External drain
capacitor C
D1
S1C31D50 TECHNICAL MANUAL
(Rev. 1.00)
IOSC oscillator circuit
IOSCEN
Clock
oscillator
IOSCFQ[1:0]
IOSCSTAIE
Figure 2.3.3.1 IOSC Oscillator Circuit Configuration
OSC1SELCR
QOSC1EN
Crystal oscillator
OSC1BUP
INV1N[1:0]
INV1B[1:0]
Oscillation startup
control circuit
Gain-controlled
Internal variable
oscillation
gate capacitor C
GI1
inverter
CGI1[2:0]
Feedback
Drain
resistor R
resistor R
F1
Internal drain capacitor C
DI1
Clock
oscillator
Figure 2.3.3.2 OSC1 Oscillator Circuit Configuration
Seiko Epson Corporation
Oscillation
stabilization
waiting circuit
IOSCSTAIF
Interrupt
control circuit
OSC1 oscillator circuit
voltage regulator
OSDRB
OSDEN
Restart
Oscillation
signal
stop
detector
OSC1WT[1:0]
Noise
Oscillation
filter
stabilization
waiting
circuit
Interrupt
control
OSC1STPIE
circuit
OSC1STAIE
D1
IOSCCLK
CPU core
OSC1CLK
OSC1STPIF
OSC1STAIF
Interrupt
controller
2-9
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