
S1C8F626 TECHNICAL MANUAL
EPSON
33
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Oscillation Circuits and Operating Mode)
5.4 Oscillation Circuits and
Operating Mode
5.4.1 Configuration of oscillation circuits
The S1C8F626 is twin clock system with two
internal oscillation circuits (OSC1 and OSC3).
The OSC3 oscillation circuit generates the main-
clock (Max. 8.2 MHz) to run the CPU and some
peripheral circuits in high speed, and the OSC1
oscillation circuit generates the sub-clock (Typ.
32.768 kHz) for low-power operation.
Figure 5.4.1.1 shows the configuration of the
oscillation circuit.
To CPU (CLK)
OSC1
oscillation circuit
Clock
switch
OSC3
oscillation circuit
To peripheral
circuit
SOSC3
Oscillation circuit
control signal
CLKCHG
CPU clock
selection signal
To some peripheral
circuit
SLEEP
status
Prescaler
(fOSC1)
(fOSC3)
Fig. 5.4.1.1 Configuration of oscillation circuits
At initial reset, OSC3 oscillation circuit is selected
for the CPU operating clock. ON/OFF switching of
the OSC3 oscillation circuit and switching of the
system clock between OSC3 and OSC1 are control-
led in software. OSC3 circuit is utilized when high
speed operation of the CPU and some peripheral
circuits become necessary. Otherwise, OSC1 should
be used to generate the operating clock and OSC3
circuit placed in a stopped state in order to reduce
current consumption.
5.4.2 Mask option
The S1C8F626 has two optional configurations
(Configuration 1 and Configuration 2) as shown in
Table 5.4.2.1 allowing selection of oscillator types of
the built-in oscillation circuit.
Table 5.4.2.1 S1C8F626 optional configurations
Option
Configuration 1
Configuration 2
OSC1
oscillation circuit
Crystal
OSC3
oscillation circuit
Crystal/Ceramic
CR
5.4.3 OSC1 oscillation circuit
The OSC1 oscillation circuit generates the 32.768
kHz (Typ.) system clock which is utilized during
low speed operation (low power mode) of the CPU
and peripheral circuits. Furthermore, even when
OSC3 is utilized as the system clock, OSC1
continues to generate the source clock for the clock
timer and stopwatch timer.
This oscillation circuit stops when the SLP instruc-
tion is executed.
Figure 5.4.3.1 shows the configuration of the OSC1
oscillation circuit.
fOSC1
VSS
OSC2
OSC1
X'tal1
CG1
SLEEP status
Fig. 5.4.3.1 OSC1 oscillation circuit (crystal oscillation)
A crystal oscillation circuit can be easily formed by
connecting a crystal oscillator X'tal1 (Typ. 32.768
kHz) between the OSC1 and OSC2 terminals along
with a trimmer capacitor CG1 (0–25 pF) between the
OSC1 terminal and VSS.
5.4.4 OSC3 oscillation circuit
The OSC3 oscillation circuit generates the system
clock when the CPU and some peripheral circuits
are in high speed operation.
This oscillation circuit stops when the SLP instruc-
tion is executed, or the SOSC3 register is set to "0".
In terms of oscillation circuit types, either crystal/
ceramic oscillation or CR oscillation can be selected
by option.
Figure 5.4.4.1 shows the configuration of the OSC3
oscillation circuit.
fOSC3
Oscillation circuit
control signal
SLEEP status
VSS
OSC4
OSC3
CD3
CG3
X'tal3
or
Ceramic
Rf
(1) Crystal/Ceramic oscillation circuit
fOSC3
Oscillation circuit
control signal
SLEEP status
OSC4
OSC3
RCR3
(2) CR oscillation circuit
Fig. 5.4.4.1 OSC3 oscillation circuit