R28 datasheet(103/473 Pages) RENESAS

103 / 473 page

R8C/28 Group, R8C/29 Group

10. Clock Generation Circuit

Rev.2.10

Sep 26, 2008

Page 84 of 441

REJ09B0279-0210

10.3

XCIN Clock (For N, D Version Only)

This clock is supplied by the XCIN clock oscillation circuit. This clock is used as the clock source for the CPU

clock, peripheral function clock. The XCIN clock oscillation circuit is configured by connecting a resonator

between the XCIN and XCOUT pins. The XCIN clock oscillation circuit includes an on-chip a feedback resistor,

which is disconnected from the oscillation circuit in stop mode in order to reduce the amount of power consumed in

the chip. The XCIN clock oscillation circuit may also be configured by feeding an externally generated clock to the

XCIN pin.

Figure 10.12 shows Examples of XCIN Clock Connection Circuits.

During and after reset, the XCIN clock stops.

The XCIN clock starts oscillating when the CM01 bit in the CM0 register is set to 1 (XCIN clock) and the CM04

bit in the CM0 register is set to 1 (XCIN-XCOUT pin).

To use the XCIN clock for the CPU clock source, set the OCD2 bit in the OCD register to 0 (selects XIN clock)

after the XCIN clock is oscillating stably.

This MCU has an on-chip feedback resistor and on-chip resistor disable/enable switching is possible by the CM12

bit in the CM1 register.

In stop mode, all clocks including the XCIN clock stop. Refer to 10.5 Power Control for details.

Figure 10.12

Examples of XCIN Clock Connection Circuits

XCIN

XCOUT

MCU

(on-chip feedback resistor)

Rd(1)

COUT

CIN

XCIN

XCOUT

MCU

(on-chip feedback resistor)

Externally derived clock

VCC

VSS

NOTE:

1. Insert a damping resistor and feedback resistor if required. The resistance will vary depending on the oscillator and

the oscillation drive capacity setting. Use the value recommended by the manufacturer 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 to the chip externally, insert a feedback resistor between

XCIN and XCOUT following the instructions.

Open

External crystal oscillator circuit

External clock input circuit

Rf(1)

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