
Rev.2.10 Apr 14, 2006 page 65 of 378
REJ09B0124-0210
M16C/6N Group (M16C/6NK, M16C/6NM) 8. Clock Generation Circuit
Figure 8.10 Examples of Sub Clock Connection Circuit
8.1.2 Sub Clock
The sub clock is generated by the sub clock oscillation circuit. This clock is used as the clock source for
the CPU clock, as well as the timer A and timer B count sources. In addition, an fC clock with the same
frequency as that of the sub clock can be output from the CLKOUT pin.
The sub clock oscillation circuit is configured by connecting a crystal resonator between pins XCIN and
XCOUT. The sub clock oscillation circuit has an on-chip feedback resistor, which is disconnected from
the oscillation circuit during stop mode in order to reduce the amount of power consumed in the chip. The
sub clock oscillation circuit may also be configured by feeding an externally generated clock to the XCIN
pin. Figure 8.10 shows an Examples of Sub Clock Connection Circuit.
After reset, the sub clock is turned off. At this time, the feedback resistor is disconnected from the oscillation
circuit.
To use the sub clock for the CPU clock, set the CM07 bit in the CM0 register to 1 (sub clock) after the sub
clock becomes oscillating stably.
During stop mode, all clocks including the sub clock are turned off. Refer to 8.4 Power Control.
NOTE:
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 XCIN and XCOUT if the oscillator manufacturer
recommends placing the resistor externally.
MCU
(On-chip feedback resistor)
MCU
(On-chip feedback resistor)
External clock
Open
VCC
VSS
XCIN
XCOUT
RCd
(1)
CCIN
CCOUT
VSS
Oscillator
XCIN
XCOUT
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