R8C datasheet(31/199 Pages) RENESAS

31 / 199 page

R8C/10 Group

Rev.1.20 Jan 27, 2006

page 21 of 180

REJ09B0019-0120

Microcomputer

(Built-in feedback resistor)

XIN

XOUT

Externally derived clock

Open

Vcc

Vss

Microcomputer

(Built-in feedback resistor)

XIN

XOUT

CIN

COUT

(Note 1)

NOTES:

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

capacity setting. Use the value recommended by the maker 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 external to the chip, insert a feedback resistor between XIN

and XOUT following the instruction.

Figure 6.4 Examples of Main Clock Connection Circuit

The following describes the clocks generated by the clock generation circuit.

6.1 Main Clock

This clock is supplied by a main clock oscillation circuit. 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 con-

sumed in the chip. The main clock oscillator circuit may also be configured by feeding an externally

generated clock to the XIN pin. Figure 6.4 shows examples of main clock connection circuit.

During reset and after reset, the main clock is turned off.

The main clock starts oscillating when the CM05 bit in the CM0 register is set to “0” (main clock on) after

setting the CM13 bit in the CM1 register to “1” (XIN- XOUT pin).

To use the main clock for the CPU clock, set the OCD2 bit in the OCD register to “0” (selecting main clock)

after the main clock becomes oscillating stably.

The power consumption can be reduced by setting the CM05 bit in the CM0 register to “1” (main clock off)

if the OCD2 bit is set to “1” (selecting on-chip oscillator clock).

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”. 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 Section 6.3, “Power Con-

trol.”

6.1 Main Clock

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