Main Clock - Renesas M16C FAMILY series Hardware Manual

M 1 6 C 2 / 8 G o r u p ( M 1 6 C
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 main clock oscillates after reset. 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, X
because the internal feedback resistor remains on, X
During stop mode, all clocks including the main clock are turned off. Refer to 7.6 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)
NOTE:
1. Insert a damping resistor if required. Resistance value varies depending on the oscillator setting.
2. The external clock should not be stopped when it is connected to the X
Figure 7.8 Examples of Main Clock Connection Circuit
R e . v 2 0 . 0 J a . n 3 , 1 2 0 0 7
R E J 0 9 B 0 0 4 7 0 - 2 0 0
2 / , 8 M 1 6 C 2 / 8 ) B
and X pins. The main clock oscillator circuit contains a feedback resistor,
IN OUT
pin. Figure 7.8 shows the examples of main clock connection circuit.
IN
C
X
IN
Oscillator
X
OUT
(1)
C
Rd
OUT
V
SS
Use resistance value recommended by the oscillator manufacturer. If the oscillator manufacturer
recommends that a feedback resistor be added to the chip externally, insert a feedback resistor
between X and X .
IN OUT
selected as the CPU clock.
page 51
f o 3 8 5
is pulled "H" to X
IN
Microcomputer
(Built-in Feedback Resistor)
IN
X
IN
X
OUT
7. Clock Generation Circuit
goes "H". Furthermore,
OUT
via the feedback resistor.
OUT
External Clock
V
CC
V
SS
Open
pin and the main clock is
IN