
2 POWER SUPPLY, RESET, AND CLOCKS
S1C31D50/D51 TECHNICAL MANUAL
Seiko Epson Corporation
2-7
(Rev. 2.00)
IOSC oscillator circuit
Inter
nal data
bu
s
IOSCEN
Clock
oscillator
Oscillation
stabilization
waiting circuit
Interrupt
control circuit
IOSCFQ[1:0]
IOSCSTAIE
IOSCSTAIF
CPU core
IOSCCLK
Figure 2.3.3.1 IOSC Oscillator Circuit Configuration
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 on the oscillation characteristics,
refer to “IOSC oscillator circuit characteristics” in the “Electrical Characteristics” chapter.
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.
Gain-controlled
oscillation
inverter
Feedback
resistor R
F1
Drain
resistor R
D1
OSC1 oscillator circuit
External gate
capacitor C
G1
Internal variable
gate capacitor C
GI1
Restart
signal
External drain
capacitor C
D1
Internal drain capacitor C
DI1
OSC1BUP
Oscillation startup
control circuit
OSC1 oscillator circuit
voltage regulator
Oscillation
stabilization
waiting circuit
Oscillation
stop detector
Noise filter
Interrupt
control circuit
INV1N[1:0]
OSC1WT[1:0]
INV1B[1:0]
OSDRB OSDEN
CGI1[2:0]
OSC1
(
)
(
)
OSC2
X’tal1
OSC1STAIE
OSC1STAIF
OSC1STPIE
OSC1STPIF
Interrupt
controller
OSC1CLK
Inter
nal data
bu
s
Crystal oscillator
OSC1EN
Selector
OSC1SELCR
Internal oscillator
Clock
oscillator
Figure 2.3.3.2 OSC1 Oscillator Circuit Configuration
Crystal oscillator
This oscillator circuit includes a gain-controlled oscillation inverter and a variable gate capacitor allowing use
of various crystal resonators (32.768 kHz typ.) with ranges from cylinder type through surface-mount type.
The oscillator circuit also includes a feedback resistor and a drain resistor, so no external parts are required
except for a crystal resonator. The embedded oscillation stop detector, which detects oscillation stop and
restarts the oscillator, allows the system to operate in safety under adverse environments that may stop the
oscillation. The oscillation startup control circuit operates for a set period of time after the oscillation is en-
abled to assist the oscillator in initiating, this makes it possible to use a low-power resonator that is difficult
to start up.
Note: Depending on the circuit board or the crystal resonator type used, an external gate capacitor C
G1
and a drain capacitor C
D1
may be required.
Internal oscillator
This 32 kHz oscillator circuit operates without any external parts.
When the internal oscillator circuit is used, set the OSC1 pin level to V
SS
and leave the OSC3 pin open.
For the recommended parts and the oscillation characteristics, refer to the “Basic External Connection Diagram”
chapter and “OSC1 oscillator circuit characteristics” in the “Electrical Characteristics” chapter, respectively.