M16C30P_07 Datasheet, PDF (65/317 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/30 SERIES

M16C/30P Group
9. Clock Generating Circuit
The following describes the clocks generated by the clock generation circuit.
9.1.1 Main Clock
This clock is used as the clock source for the CPU and peripheral function clocks. 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 XIN and XOUT pins. The main 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 main clock oscillator circuit may also be configured by feeding an externally
generated clock to the XIN pin. Figure 9.5 shows the examples of 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 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, XOUT goes “H”. Furthermore, because the internal feedback resistor remains on,
XIN is pulled “H” to XOUT via the feedback resistor. Note that if an externally generated clock is fed into the
XIN pin, the main clock cannot be turned off by setting the CM05 bit to “1” unless the sub clock is chosen 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 9.4 Power Control.
Microcomputer
(Built-in Feedback Resistor)
XIN
Oscillator
XOUT
VSS
Rd⁽¹⁾
CIN
COUT
Microcomputer
(Built-in Feedback Resistor)
XIN
External clock
VCC1
VSS
XOUT Open
NOTES :
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 XIN and XOUT if the oscillator manufacturer recommends placing the resistor externally.
Figure 9.5 Examples of Main Clock Connection Circuit
Rev.1.22 Mar 29, 2007 Page 49 of 291
REJ09B0179-0122