Sub Clock - Renesas M16C/60 Series Hardware Manual

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M16C/6N5 Group

(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 f
frequency as that of the sub clock can be output from the CLK
The sub clock oscillator circuit is configured by connecting a crystal resonator between the X
pins. The sub clock oscillator circuit contains 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 sub clock
oscillator circuit may also be configured by feeding an externally generated clock to the X
1.8.10 shows the examples of sub clock connection circuit.
After reset, the sub clock is turned off. At this time, the feedback resistor is disconnected from the oscillator
circuit.
To use the sub clock for the CPU clock, set the CM07 bit of 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 "power control".
Note: Insert a damping resistor if required. The resistance will vary depending on the
Figure 1.8.10 Examples of Sub Clock Connection Circuit
Rev.1.00 2003.05.30 page 51
Microcomputer
(Built-in feedback resistor)
X X
CIN COUT
(Note)
R
Cd
C C
CIN COUT
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
following the instruction.
Clock Generation Circuit
clock with the same
C
pin.
OUT
Microcomputer
(Built-in feedback resistor)
X X
CIN COUT
Open
Externally derived clock
Vcc
Vss
and X
CIN COUT
and X
CIN COUT
pin. Figure
CIN