M32CSLASH86 datasheet(103/505 Pages) RENESAS

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Page 80

9. Clock Generation Circuit

)

(

9.1.1 Main Clock

Main clock oscillation circuit generates the main clock. The main clock becomes clock source of the CPU

clock and peripheral function clock.

The main clock oscillation circuit is configured by connecting an oscillator or resonator between the XIN

and XOUT pins. The circuit has a built-in feedback resistor. The feedback resistor is separated from the

oscillation circuit in stop mode to reduce power consumption. An external clock can be applied to the XIN

pin in the main clock oscillation circuit. Figure 9.9 shows an example of a main clock circuit connection.

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

lator manufacturer.

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

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

switching the CPU clock source to the sub clock or on-chip oscillator clock. In this case, the clock applied

to XOUT becomes high ("H"). XIN is pulled up by XOUT via the feedback resistor which remains on. When

an external clock is applied 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

External Clock

XIN

XOUT

Open

VCC

VSS

NOTES:

1. Place a damping resistor if required. Resistance values vary depending on the oscillator setting.

Use values recommended by each oscillator manufacturer.

Place a feedback resistor between XIN and XOUT if the oscillator manufacturer recommends

placing the resistor externally.

Oscillator

(1)

CIN

COUT

XIN

XOUT

Microcomputer

(Built-in Feedback Resistor)

Microcomputer

(Built-in Feedback Resistor)

VSS

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