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8 OSCILLATION CIRCUITS
8.1 Configuration of Oscillation
Circuits
The S1C88655 is twin clock system with two
internal oscillation circuits (OSC1 and OSC3).
The OSC3 oscillation circuit generates the main-
clock to run the CPU and some peripheral circuits
in high speed, and the OSC1 oscillation circuit
generates the sub-clock for low-power operation.
Figure 8.1.1 shows the configuration of the oscilla-
tion circuit.
OSC1
oscillation
circuit
OSC1ON
SOSC1
OSC1ON
WDT
control
enable
CLKCHG
SLEEP
OSC3ON
status
control
SOSC3
OSC3ON
OSC3
oscillation
circuit
Fig. 8.1.1 Configuration of oscillation circuits
At initial reset, the OSC3 oscillation circuit is
selected for the CPU operating clock source.
Turning the OSC3 oscillation circuit ON/OFF and
switching of the system clock between OSC3 and
OSC1 are controlled in software. The OSC3 oscilla-
tion circuit is utilized when the CPU and some
peripheral circuits must be operated in high speed.
Otherwise, OSC1 should be used to generate the
operating clock with the OSC3 oscillation circuit
stopped in order to reduce current consumption.
S1C88655 TECHNICAL MANUAL
f
OSC1
Divider
To peripheral
circuit
OSC1ON status
Clock
switching
To CPU
control
OSC3ON status
f
OSC3
Divider
To peripheral
circuit
8.2 Mask Option
OSC1 oscillation circuit
Crystal oscillation circuit
CR oscillation circuit
OSC3 oscillation circuit
Crystal oscillation circuit
Ceramic oscillation circuit
CR oscillation circuit
The OSC1 oscillator types can be selected from
crystal and CR by mask option. The OSC3 oscillator
types can be selected from crystal, ceramic, and CR
by mask option.
EPSON
8 OSCILLATION CIRCUITS
55
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