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M16C/62P Group (M16C/62P, M16C/62PT)
The following describes the clocks generated by the clock generation circuit.
10.1.1 Main Clock
This clock is used as the clock source for the CPU and peripheral function clocks. This clock is used as
the clock source for the CPU and peripheral function clocks. The main clock oscillator circuit is config-
ured by connecting a resonator between the XIN and XOUT pins. The main clock oscillator circuit con-
tains a feedback resistor, which is disconnected from the oscillator circuit during stop mode in order to
reduce the amount of power consumed in the chip. The main clock oscillator circuit may also be config-
ured by feeding an externally generated clock to the XIN pin. Figure 10.7 shows the examples of main
clock connection circuit.
After reset, the main clock divided by 8 is selected for the CPU clock.
The power consumption in the chip can be reduced by setting the CM05 bit in the CM0 register to "1"
(main clock oscillator circuit turned off) after switching the clock source for the CPU clock to a sub clock or
on-chip oscillator clock. In this case, XOUT goes "H". Furthermore, because the internal feedback
resistor remains on, XIN is pulled "H" to XOUT via the feedback resistor. Note that if an externally
generated clock is fed into the XIN pin, the main clock cannot be turned off by setting the CM05 bit to "1,"
unless the sub clock is chosen as a CPU clock. If necessary, use an external circuit to turn off the clock.
During stop mode, all clocks including the main clock are turned off. Refer to 10.4 Power Control.
Microcomputer
(Built-in feedback resistor)
XIN
CIN
NOTES:
1. Place a damping resistor if required. The resistance will vary depending on the oscillator and the oscillation drive
capacity setting. Use the value recommended by each oscillator the oscillator manufacturer.
When the oscillation drive capacity is set to low, check that oscillation is stable. Also, place a feedback resistor
between XIN and XOUT if the oscillator manufacturer recommends placing the resistor externally.
Figure 10.7 Examples of Main Clock Connection Circuit
R
e
. v
2
3 .
0
S
e
p
0
, 1
2
0
0
4
R
E
J
0
9
B
0
1
8
5
0 -
2
3
0
Z
XOUT
(1)
Rd
COUT
page 72
f o
3
6
4
10. Clock Generating Circuit
Microcomputer
(Built-in feedback resistor)
XIN
XOUT
Open
Externally derived clock
VCC1
VSS
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