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M16C/29 Group
The following describes the clocks generated by the clock generation circuit.
7.1 Main Clock
The main clock is generated by the main clock oscillation circuit. This clock is used as the clock source for
the CPU and peripheral function clocks. The main clock oscillator circuit is configured by connecting a
resonator between the X
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 configured by feeding an externally
generated clock to the X
The power consumption in the chip can be reduced by setting the CM05 bit of 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, X
on, X
is pulled "H" to X
IN
During stop mode, all clocks including the main clock are turned off. Refer to "power control".
If the main clock is not used, it is recommended to connect the XIN pin to VCC to reduce power consump-
tion during reset.
Microcomputer
(Built-in feedback resistor)
X
IN
C
IN
Note: Insert a damping resistor if required. The resistance will vary depending on the oscillator and the oscillation drive
capacity setting. Use the value recommended by the maker of the oscillator.
When the oscillation drive capacity is set to low, check that oscillation is stable. Also, if the oscillator manufacturer's
data sheet specifies that a feedback resistor be added external to the chip, insert a feedback resistor between X
and X
OUT
Figure 7.1.1. Examples of Main Clock Connection Circuit
Rev.1.00 Nov 01,2004
REJ09B0101-0100Z
and X
pins. The main clock oscillator circuit contains a feedback resistor,
IN
OUT
pin. Figure 7.1.1 shows the examples of main clock connection circuit.
IN
goes "H". Furthermore, because the internal feedback resistor remains
OUT
via the feedback resistor.
OUT
X
OUT
(Note)
R
d
C
OUT
following the instruction.
page 45 of 402
7. Clock Generation Circuit
Microcomputer
(Built-in feedback resistor)
X
X
IN
OUT
Open
Externally derived clock
V
CC
Vss
IN
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