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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 enabled 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
and a drain capacitor C
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
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.
OSC3 oscillator circuit
The OSC3 oscillator circuit is a crystal/ceramic oscillator, internal oscillator that generates a high-
speed clock.
Figure 2.3.3.3 shows the configuration of the OSC3 oscillator circuit.
Internal gate
capacitor C
External gate
OSC3
capacitor C
G3
X'tal3/
I/O
Ceramic3
port
External drain
OSC4
capacitor C
D3
Internal drain
capacitor C
OSC1
oscillator
circuit
Crystal/Ceramic Mode
This oscillator circuit includes a feedback resistor and a drain resistor, so no external part is
required except for a crystal/ceramic resonator. The embedded gain-controlled inverter allows
selection of the resonator from a wide frequency range. For the recommended parts and the
oscillation characteristics, refer to the "Basic External Connection Diagram" chapter and the "Electrical
Characteristics" chapter, respectively.
2-10
may be required.
D1
OSC3 oscillator circuit
GI3C
Gain-
controlled
inverter
Peripheral
I/O
function 4
VSS
Feedback
Drain resistor
resistor R
F3
VSS
DI3C
Auto-
trimming
OSC1CLK
circuit
OSC3STM
Figure 2.3.3.3 OSC3 Oscillator Circuit Configuration
Seiko Epson Corporation
and leave the OSC3 pin open.
SS
OSC3EN
OSC3INV[1:0]
OSC3WT[2:0]
Oscillation
Noise
stabilization
waiting
filter
circuit
R
D3
OSC3STAIE
Interrupt
OSC3TEDIE
control circuit
OSC3TERIE
G1
OSC3CLK
OSC3STAIF
OSC3TEDIF
OSC3TERIF
CPU core
S1C31D50 TECHNICAL MANUAL
(Rev. 1.00)
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