R8C23 datasheet(91/549 Pages) RENESAS

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R8C/22 Group, R8C/23 Group

10. Clock Generation Circuit

Rev.2.00 Aug 20, 2008

Page 71 of 501

REJ09B0251-0200

10. Clock Generation Circuit

The clock generation circuit has:

• XIN clock oscillation circuit

• Low-speed on-chip oscillator

• High-speed on-chip oscillator

Table 10.1 lists Specifications of Clock Generation Circuit. Figure 10.1 shows a Clock Generation Circuit. Figures

10.2 to 10.8 show clock-associated registers.

NOTES:

1. These pins can be used as P4_6 and P4_7 when using the on-chip oscillator clock as the CPU

clock while the XIN clock oscillation circuit is not used.

2. Set the CM05 bit in the CM0 register to 1 (main clock stops) and the CM13 bit in the CM1 register to

1 (XIN-XOUT pin) when the external clock is input.

3. The clock frequency is automatically set to up to 20 MHz by a driver when using the high-speed on-

chip oscillator as the CPU clock source.

Table 10.1

Specifications of Clock Generation Circuit

Item

XIN Clock

Oscillation Circuit

On-Chip Oscillator

High-Speed On-Chip Oscillator

Low-Speed On-Chip Oscillator

Use of Clock

• CPU clock source

• Peripheral

function clock

source

• CPU clock source

• Peripheral function clock

source

• CPU and peripheral function

clock sources when XIN clock

stops oscillating

• CPU clock source

• Peripheral function clock

source

• CPU and peripheral function

clock sources when XIN clock

stops oscillating

Clock Frequency 0 to 20 MHz

Approx. 40 MHz(3)

Approx. 125 kHz

Connectable

Oscillator

•Ceramic

resonator

• Crystal oscillator

−−

Oscillator

Connect Pins

XIN, XOUT(1)

−(1)

Oscillation Stop,

Restart Function

Usable

Oscillator Status

After Reset

Stop

Oscillate

Others

Externally

generated clock

can be input(2)

−−

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