
S1C88409 TECHNICAL MANUAL
EPSON
55
CHAPTER 5: PERIPHERAL CIRCUITS AND OPERATION (Oscillation Circuit)
When crystal oscillation is selected, the crystal
oscillation circuit can be configured simply by
connecting a crystal oscillator X'tal1 (Typ. 32.768
kHz) between the OSC1 and OSC2 terminals and a
trimmer capacitor CG1 (5–25pF) between the OSC1
terminal and VSS.
For the CG1, the built-in capacitor can also be
selected by mask option.
When CR oscillation is selected, the CR oscillation
circuit can be configured by connecting a resistor
between the OSC1 and OSC2 terminals.
When external clock input is selected, open the
OSC2 terminal and input a square wave clock to
the OSC1 terminal.
5.4.4 OSC3 oscillation circuit
The OSC3 oscillation circuit generates the system
clock for the CPU and peripheral circuits (serial
interface, programmable timer, A/D converter, etc.).
The OSC3 oscillation circuit stops when the SLP
instruction is executed, or the OSCC register is set
to "0".
Either "Crystal oscillation", "Ceramic oscillation",
"CR oscillation" or "External clock input" can be
selected by mask option as a kind of OSC3 oscilla-
tion circuit.
Figure 5.4.4.1 shows the structure of the OSC3
oscillation circuit.
VSS
OSC4
OSC3
Rf
CD2
CG2
X'tal2
or
Ceramic
fOSC3
Oscillation circuit
control signal
SLEEP status
(1) Crystal/Ceramic oscillation circuit
Oscillation circuit
control signal
SLEEP status
OSC4
OSC3
RCR3
fOSC3
(2) CR oscillation circuit
OSC4
OSC3
External
clock
N.C.
VSS
VDD
Oscillation circuit
control signal
SLEEP status
fOSC3
(3) External clock input
Fig. 5.4.4.1 OSC3 oscillation circuit
When crystal/ceramic oscillation circuit is se-
lected, the crystal or ceramic oscillation circuit is
configured by connecting either a crystal oscillator
(X'tal2) or a ceramic oscillator (Ceramic) and a
feedback resistor (Rf) between the OSC3 and OSC4
terminals and two capacitors (CG2, CD2) between
the OSC3 terminal and VSS, and between the OSC4
terminal and VSS, respectively.
When CR oscillation is selected, the CR oscillation
circuit can be configured by connecting a resistor
(RCR3) between the OSC3 and OSC4 terminals.
When external clock input is selected, open the
OSC4 terminal and input a square wave clock to
the OSC3 terminal.
When the OSC3 oscillation circuit is not used,
select external clock input by mask option, and
pull down the OSC3 terminal to VSS.
The maximum frequency of the clock, which can
be generated by the OSC3 oscillation circuit or can
be input to the OSC3 oscillation circuit, is limited
depending on the supply voltage as shown in
Table 5.4.4.1.
Table 5.4.4.1 Limit of OSC3 clock frequency depending
on supply voltage
Operable voltage range (VDD)
1.8 V–5.5 V
2.6 V–5.5 V
3.5 V–5.5 V
4.5 V–5.5 V
Max. operable frequency
1.1 MHz
4.4 MHz
6.6 MHz
8.8 MHz