2 POWER SUPPLY, RESET, AND CLOCKS
2-8
Seiko Epson Corporation
S1C31D50/D51 TECHNICAL MANUAL
(Rev. 2.00)
OSC3 oscillator circuit
The OSC3 oscillator circuit is a high-speed oscillator circuit that allows software to select the oscillator type
from two different types shown below. Figure 2.3.3.3 shows the configuration of the OSC3 oscillator circuit.
OSC3 oscillator circuit
Gain-
controlled
inverter
Feedback
resistor R
F3
Drain resistor
R
D3
Crystal/ceramic oscillator
OSC3EN
Oscillation
stabilization
waiting circuit
Noise
filter
Selector
OSC3INV[1:0]
OSC3WT[2:0]
OSC3
OSC4
Interrupt
controller
OSC3CLK
OSC3FQ[1:0]
OSC3MD
(
)
(
)
X’tal3/
Ceramic3
V
SS
V
SS
Inter
nal data
bu
s
Internal oscillator
External gate
capacitor C
G3
Internal gate
capacitor C
GI3C
Internal drain
capacitor C
DI3C
Peripheral
I/O
function 4
External drain
capacitor C
D3
Clock
oscillator
I/O
port
Interrupt
control
circuit
OSC3STAIE
OSC3STAIF
OSC3TEDIF
OSC3TEDIE
OSC1CLK
Auto-
trimming
circuit
OSC3STM
OSC1
oscillator
circuit
Figure 2.3.3.3 OSC3 Oscillator Circuit Configuration
Crystal/ceramic oscillator
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.
Internal oscillator
This oscillator circuit features a fast startup and no external parts are required for oscillating. The
OSC3CLK frequency can be selected using the CLGOSC3.OSC3FQ[1:0] bits. This oscillator circuit
is equipped with an auto-trimming function that automatically adjusts the frequency. This helps reduce
frequency deviation due to unevenness in manufacturing quality, temperature, and changes in voltage. For
more information on the auto-trimming function, refer to “OSC3 oscillation auto-trimming function” in this
chapter.
For the recommended parts and the oscillation characteristics, refer to the “Basic External Connection Diagram”
chapter and “OSC3 oscillator circuit characteristics” in the “Electrical Characteristics” chapter, respectively.
EXOSC clock input
EXOSC is an external clock input circuit that supports square wave and sine wave clocks. Figure 2.3.3.4 shows
the configuration of the EXOSC clock input circuit.
EXOSC clock
input circuit
Input control
circuit
EXOSCEN
EXOSC
EXOSCCLK
Inter
nal data
bu
s
Figure 2.3.3.4 EXOSC Clock Input Circuit
EXOSC has no oscillation stabilization waiting circuit included, therefore, it must be enabled when a stabilized
clock is being supplied. For the input clock characteristics, refer to “EXOSC external clock input characteris-
tics” in the “Electrical Characteristics” chapter.