
S1C8F360 TECHNICAL MANUAL
EPSON
41
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Oscillation Circuits and Operating Mode)
5.4.4 OSC3 oscillation circuit
The OSC3 oscillation circuit generates the system
clock when the CPU and some peripheral circuits
(output port, serial interface and programmable
timer) are in high speed operation.
This oscillation circuit stops when the SLP instruc-
tion is executed, or the OSCC register is set to "0".
In terms of oscillation circuit types, either crystal /
ceramic oscillation or CR oscillation can be selected
by mask option.
Figure 5.4.4.1 shows the configuration of the OSC3
oscillation circuit.
5.4.5 Operating mode
You can select three types of operating modes using
software, to obtain a stable operation and good
characteristics (operating frequency and current
consumption) over a broad operation voltage. Here
below are indicated the features of the respective
modes.
Normal mode (VDD = 2.4 V–5.5 V)
This mode is set following the initial reset. It
permits the OSC3 oscillation circuit (Max. 4.2
MHz) to be used and also permits relative low
power operation.
Low power mode (VDD = 2.0 V–3.5 V)
This is a lower power mode than the normal
mode. It makes ultra-low power consumption
possible by operation on the OSC1 oscillation
circuit, although the OSC3 circuit cannot be
used.
High speed mode (VDD = 3.5 V–5.5 V)
This mode permits higher speed operation than
the normal mode. Since the OSC3 oscillation
circuit (Max. 8.2 MHz) can be used, you should
use this mode, when you require operation at
4.2 MHz or more. However, the current con-
sumption will increase relative to the normal
mode.
Using software to switch over among the above
three modes to meet your actual usage circum-
stances will make possible a low power system. For
example, you will be able to reduce current con-
sumption by switching over to the normal mode
when using the OSC3 as the CPU clock and,
conversely, changing over to the low power mode
when using the OSC1 as the CPU clock (OSC3
oscillation circuit is OFF).
Note: Do not turn the OSC3 oscillation circuit ON
in the low power mode.
Do not switch over the operating mode
(normal mode
high speed mode) in the
OSC3 oscillation circuit ON status, as this
will cause faulty operation.
You can not use two modes, the low power
mode and the high speed mode on one
application, with respect to the operating
voltages.
VSS
OSC4
OSC3
Rf
CD2
CG2
fOSC3
Oscillation circuit
control signal
SLEEP status
X'tal 2
or
Ceramic
Oscillation circuit
control signal
SLEEP status
OSC4
OSC3
RCR3
fOSC3
(1) Crystal/Ceramic oscillation circuit
(2) CR oscillation circuit
Fig. 5.4.4.1 OSC3 oscillation circuit
When crystal/ceramic oscillation circuit is selected,
the crystal or ceramic oscillation circuit are formed
by connecting either a crystal oscillator (X'tal2) or a
combination of ceramic oscillator (Ceramic) and
feedback resistor (Rf) between OSC3 and OSC4
terminals and connecting 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 is formed merely by connecting a resistor
(RCR3) between OSC3 and OSC4 terminals.