M16C30P_07 Datasheet, PDF (66/317 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/30 SERIES

M16C/30P Group
9. Clock Generating Circuit
9.1.2 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 fc clock with the same frequency
as that of the sub clock can be output from the CLKOUT pin.
The sub clock oscillator circuit is configured by connecting a crystal resonator between the XCIN and XCOUT
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 XCIN pin.
Figure 9.6 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 in the 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 9.4 Power Control.
Microcomputer
(Built-in Feedback Resistor)
XCIN
Oscillator
XCOUT
VSS
RCd⁽¹⁾
CCIN
CCOUT
Microcomputer
(Built-in Feedback Resistor)
XCIN
External clock
VCC1
VSS
XCOUT 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 XCIN and XCOUT if the oscillator manufacturer recommends placing the resistor externally.
Figure 9.6 Examples of Sub Clock Connection Circuit
Rev.1.22 Mar 29, 2007 Page 50 of 291
REJ09B0179-0122