R5F3640MNFB datasheet(102/398 Pages) RENESAS

102 / 398 page

REJ09B0392-0064 Rev.0.64

Oct 12, 2007

Page 81 of 373

Under development

Preliminary Specification

Specification in this preliminary version is subject to change.

M16C/64 Group

10. Clock Generation Circuit

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

10.1.1

Main Clock

This clock is provided by the main clock oscillation circuit and used as the clock source for the CPU and

peripheral function clocks. The main clock oscillation circuit is configured by connecting a resonator

between pins XIN and XOUT. The main clock oscillation circuit contains a feedback resistor, which is dis-

connected from the oscillation circuit during stop mode in order to reduce the amount of power consumed

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

clock to the XIN pin. Figure 10.7 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 oscillation circuit turned off) after switching the clock source for the CPU clock to a sub clock or 125

kHz on-chip oscillation 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 10.4 “Power Control” for

details.

Figure 10.7

Examples of Main Clock Connection Circuit

NOTE :

1. Place a damping resistor if required. The resistance will vary depending on the

oscillator and the oscillation drive capacity setting. Use the value recommended by

each oscillator manufacturer.

When the oscillation drive capacity is set to low, check if oscillation is stable at low.

Also, place a feedback resistor between XIN and XOUT if the oscillator manufacturer

recommends placing the resistor externally.

External clock

Open

VCC1

VSS

Microcomputer

(Built-in feedback resistor)

XIN

XOUT

Rd (1)

CIN

COUT

VSS

Oscillator

Microcomputer

(Built-in feedback resistor)

XIN

XOUT

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