R28 datasheet(91/473 Pages) RENESAS

91 / 473 page

R8C/28 Group, R8C/29 Group

10. Clock Generation Circuit

Rev.2.10

Sep 26, 2008

Page 72 of 441

REJ09B0279-0210

10. Clock Generation Circuit

The clock generation circuit has:

• XIN clock oscillation circuit

• XCIN clock oscillation circuit (For N, D version only)

• Low-speed on-chip oscillator

• High-speed on-chip oscillator

However, use one of the XIN clock oscillation circuit or the XCIN clock oscillation circuit because they share the

XIN/XCIN pin and the XOUT/XCOUT pin. (For J, K version, the XCIN clock oscillation circuit cannot be used.)

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

10.2 to 10.9 show clock associated registers. Figure 10.10 shows a Procedure for Enabling Reduced Internal Power

Consumption Using VCA20 bit.

NOTES:

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

XIN clock oscillation circuit and XCIN clock oscillation circuit is not used.

2. Set the CM01 bit in the CM0 register to 0 (XIN clock), the CM05 bit in the CM0 register to 1 (XIN clock stopped),

and the CM13 bit in the CM1 register to 1 (XIN-XOUT pin) when an external clock is input.

3. When 32.768 kHz is used as an external clock, set the CM01 bit in the CM0 register to 1 (XCIN clock). In other

cases, set the CM01 bit in the CM0 register to 0 (XIN clock).

4. Set the CM01 bit in the CM0 register to 1 (XCIN clock) and the CM04 bit in the CM0 register to 1 (XCIN clock

oscillator) when an external clock is input.

5. The clock frequency is automatically set to up to 20 MHz by a divider 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

XCIN Clock Oscillation

Circuit

(For N, D Version Only)

On-Chip Oscillator

High-Speed On-Chip

Oscillator

Low-Speed On-Chip

Oscillator

Applications

• CPU clock source

• Peripheral function

clock source

• 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

32.768 kHz

Approx. 40 MHz(5)

Approx. 125 kHz

Connectable

oscillator

• Ceramic resonator

• Crystal oscillator

−−

Oscillator

connect pins

XIN, XOUT(1)

XCIN, XCOUT(1)

−(1)

Oscillation stop,

restart function

Usable

Oscillator status

after reset

Stop

Oscillate

Others

• Externally generated

clock can be input(2, 3)

• On-chip feedback

resistor RfXIN

(connected/ not

connected, selectable)

• Externally generated

clock can be input(4)

• On-chip feedback

resistor RfXCIN

(connected/ not

connected,

selectable)

−−

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