M16CSLASH29 datasheet(78/499 Pages) RENESAS

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7. Clock Generation Circuit

page 54

Figure 7.8 Examples of Main Clock Connection Circuit

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

7.1 Main Clock

The main clock is generated by the 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

consumed in the chip. The main clock oscillator circuit may also be configured by feeding an exter nally

generated clock to the XIN pin. Figure 7.8 shows the examples of main clock connection circuit.

The power consumption in the chip can be reduced by setting the CM05 bit in the CM0 register to 1 (main

clock oscillator circuit turned off) after switching the clock source for the CPU clock to a sub clock or on-chip

oscillator clock. In this case, XOUT goes “H”. Furthermore, because the internal feedback resistor remains

on, XIN is pulled “H” to XOUT via the feedback resistor.

During stop mode, all clocks including the main clock are turned off. Refer to “power control”.

If the main clock is not used, it is recommended to connect the XIN pin to VCC to reduce power consump-

tion during reset.

External Clock

XIN

XOUT

Open

VCC

VSS

NOTE:

1. Insert a damping resistor if required. Resistance value varies depending on the oscillator setting.

Use resistance value 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.

2. The external clock should not be stopped when it is connected to the XIN pin and the main clock is

selected as the CPU clock.

Oscillator

Rd(1)

CIN

COUT

XIN

XOUT

MCU

(Built-in Feedback Resistor)

MCU

(Built-in Feedback Resistor)

VSS

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