M32C83T datasheet(97/527 Pages) RENESAS

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Page 74

8. Clock Generation Circuit

)

(

8.1.1 Main Clock

Main clock oscillation circuit generates the main clock. The main clock becomes a clock source for 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. The externally generated clock can be input

to the XIN pin in the main clock oscillation circuit. Figure 8.9 shows an example of a main clock circuit

connection. Circuit constants vary with each oscillator. Use the circuit constant recommended by each

oscillator manufacturer.

The main clock divided-by-eight becomes the CPU clock 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, XOUT becomes

"H". XIN is pulled up by XOUT via the feedback resistor which remains on. When an externally generated

clock is input to the XIN pin, the main clock does not stop even if the CM05 bit is set to "1". Terminate main

clock operation externally if necessary.

All clocks, including the main clock, stop in stop mode. Refer to 8.5 Power Consumption Control for details.

Figure 8.9 Main Clock Circuit Connection

External Clock

XIN

XOUT

Open

VCC

VSS

NOTE:

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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