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7 Oscillator (OSC)
7.1 Configuration of OSC Module
The S1C17704 has two built-in oscillators (OSC3 and OSC1). The OSC3 oscillator generates the main clock (Max.
8.2 MHz) for operating the S1C17 Core and peripheral circuits at high speed. The OSC1 oscillator generates the
sub clock (Typ. 32.768 kHz) for operating timers and for power saving operations.
At initial reset, the OSC3 clock is selected as the system clock.
The oscillators can be turned on and off and the system clock can be switched between OSC1 and OSC3 with
software.
The OSC module allows the software to turn the oscillators on and off and to switch the system clock source
between OSC1 and OSC3.
Furthermore, the clocks generated in the OSC module can be output outside the IC.
Figure 7.1.1 shows the structure of the clock system and the OSC3 module.
SLEEP, On/Off control
OSC3
OSC3
oscillator
(8.2 MHz)
OSC4
FOUT3
FOUT3
output circuit
On/Off control
SLEEP, On/Off control
OSC1
OSC1
oscillator
(32.768 kHz)
OSC2
FOUT1
FOUT1
output circuit
On/Off control
Noise filter
RESET
On/Off control
Noise filter
NMI
On/Off control
OSC3
Current consumption can be reduced by controlling the clocks according to the processing requirements as well as by
using the standby mode. For methods to reduce current consumption, see Appendix C, "Power Saving."
S1C17704 TECHNICAL MANUAL
OSC
wakeup
Clock source select
Wait circuit for
OSC3
wakeup
OSC1
Divider
(1/1–1/4)
Division ratio select
S1C17 Core
S1C17 Core
Clock source select
Divider
(1/32–1/512)
OSC1
Division ratio select
Figure 7.1.1 Structure of the OSC Module
Gear select
System
clock
Clock gear
(1/1–1/8)
On/Off control
Gate
On/Off control
Gate
Divider
OSC1
(1/128)
Gate
(1/1–1/32)
Division ratio select
On/Off control
Gate
On/Off control
EPSON
7 OSCILLATOR (OSC)
CLG
HALT
Gate
CCLK
S1C17 Core
Gate
Internal bus, RAM,
BCLK
Flash
HALT
ITC, T16, T8F,
UART, SPI, I2C,
T16E, P, MISC,
PCLK
VD1, SVD, REMC,
Control registers
(CT, SWT, WDT,
T8OSC1, LCD)
PSC
T8F, T16, T16E,
Divider
REMC, P, UART,
(1/1–1/16K)
SPI, I2C
CLK_256Hz
CT, SWT, WDT
T8OSC1
SVD
LCLK
LCD
7-1
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