Main Clock - Renesas M16C/60 Series Hardware Manual

Under development
This document is under development and its contents are subject to change.
M16C/6N5 Group
The following describes the clocks generated by the clock generation circuit.

(1) Main Clock

This clock is used as the clock source for the CPU and peripheral function clocks. The main clock oscilla-
tor circuit is configured by connecting a resonator between the X
tor 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 main clock oscillator circuit may also
be configured by feeding an externally generated clock to the X
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 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 ring
oscillator clock. In this case, X
on, X is pulled "H" to X
IN
the X pin, the main clock cannot be turned off by setting the CM05 bit to "1" unless the sub clock is
IN
selected 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 "power control".
(Built-in feedback resistor)
X
Note: Insert a damping resistor if required. The resistance will vary depending on the
Figure 1.8.9 Examples of Main Clock Connection Circuit
Rev.1.00 2003.05.30 page 50
goes "H". Furthermore, because the internal feedback resistor remains
OUT
via the feedback resistor. Note, that if an externally generated clock is fed into
OUT
Microcomputer
X
IN OUT
(Note)
R
d
C
IN C
OUT
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
and X pins. The main clock oscilla-
IN OUT
pin. Figure 1.8.9 shows the examples of
IN
Microcomputer
(Built-in feedback resistor)
X X
IN OUT
Open
Externally derived clock
Vcc
Vss
and X
IN OUT