Main Clock - Renesas M16C FAMILY Hardware Manual

Under development
Preliminary specification
Specifications in this manual are tentative and subject to change.
R8C/11 Group
The following describes the clocks generated by the clock generation circuit.

6.1 Main Clock

This clock is supplied by a 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
tor, 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
After reset, the main clock is turned off.
The main clock starts oscillating when the CM05 bit in the CM0 register is set to "0" (main clock on)
after setting the CM13 bit in the CM1 register to "1" (X
To use the main clock for the CPU clock, set the OCD2 bit in the OCD register to "0" (selecting main
clock) after the main clock becomes oscillating stably.
The power consumption can be reduced by setting the CM05 bit in the CM0 register to "1" (main clock
off) if the OCD2 bit is set to "1" (selecting ring oscillator clock).
Note that if an externally generated clock is fed into the X
setting the CM05 bit to "1". 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 Section 6.4, "Power
Control."
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 6.5 Examples of Main Clock Connection Circuit
Rev.0.91 2003 Sep 08
and X pins. The main clock oscillator circuit contains a feedback resis-
IN OUT
pin. Figure 6.5 shows examples of main clock connection circuit.
IN
X
OUT
(Note)
R
d
C
OUT
following the instruction.
page 33 of 184
- X pin).
IN OUT
pin, the main clock cannot be turned off by
IN
Microcomputer
(Built-in feedback resistor)
X
IN
Externally derived clock
Vcc
Vss
6.1 Main Clock
X
OUT
Open
IN