M32CSLASH8A datasheet(95/372 Pages) RENESAS

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M32C/8A Group

9. Clock Generation Circuits

Rev.1.00

Jul 15, 2007

Page 78 of 352

REJ09B0385-0100

9.1.1

Main Clock

Main clock oscillation circuit generates the main clock. The main clock is used as the clock source for the CPU

clock and peripheral function clocks.

The main clock oscillation circuit is configured by connecting an oscillator between the XIN and XOUT pins.

The circuit has an on-chip feedback resistor. The feedback resistor is disconnected from the oscillation circuit in

stop mode to reduce power consumption. The main clock oscillation circuit may also be configured by feeding

an externally generated clock to the XIN pin. Figure 9.9 shows examples of main clock circuit connection.

Circuit constants vary depending on each oscillator. Use the circuit constant recommended by each oscillator

manufacturer.

The main clock divided-by-eight becomes the CPU clock source after reset.

To reduce power consumption, set the CM05 bit in the CM0 register to 1 (main clock stopped) after the sub

clock or on-chip oscillator clock is selected as the CPU clock sources. In this case, the XOUT pin outputs an

“H” signal. The XIN pin is pulled up to the XOUT pin via the feedback resistor which remains on. When an

external clock is input to the XIN pin, do not set the CM05 bit to 1.

All clocks, including the main clock, stop in stop mode. Refer to 9.5 Power Consumption Control for details.

Figure 9.9

Main Clock Circuit Connection

XIN

XOUT

Oscillator

CIN

COUT

Rd(1)

MCU

(On-chip feedback resistor)

XIN

XOUT

MCU

(On-chip feedback resistor)

Open

Externally generated clock

VCC

VSS

NOTE:

1. Insert a damping resistor if required. Resistance values vary depending on the oscillator setting. Use the resistance values

recommended by the oscillator manufacturer.

If the oscillator manufacturer recommends that a feedback resistor be added to the chip externally, insert a feedback

resistor between XIN and XOUT following the instructions.

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