M32CSLASH8B datasheet(93/406 Pages) RENESAS

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M32C/8B Group

9. Clock Generation Circuits

Preliminary specification

Specifications in this manual are tentative and subject to change.

REJ09B0450-0050 Rev.0.50 Oct 31, 2008

Page 76 of 385

9.1.2

Sub Clock

Sub clock oscillation circuit generates the sub clock. The sub clock is used as the clock source for the CPU

clock and for timer A and timer B. fC, which has the same frequency as the sub clock can be output from the

CLKOUT pin.

The sub clock oscillation circuit is configured by connecting a crystal oscillator between the XCIN and

XCOUT 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 sub clock oscillation circuit may also be

configured by feeding an externally generated clock to the XCIN pin. Figure 9.11 shows an example of sub

clock circuit connection. Circuit constants vary depending on each oscillator. Use the circuit constant

recommended by each oscillator manufacturer.

The sub clock is stopped after reset, and the feedback resistor is disconnected from the oscillation circuit. To

start oscillating the sub clock oscillation circuit, set both the PD8_7 and PD8_6 bits in the PD8 register to 0

(input mode), the PU25 bit in the PUR2 register to 0 (not pulled up), and then the CM04 bit in the CM0 register

to 1 (XCIN-XCOUT oscillation function). To input the externally generated clock to the XCIN pin, set the

PD8_7 bit to 0, the PU25 bit to 0, and then the CM04 bit to 1. A clock input to the XCIN pin becomes the clock

source for the sub clock.

When the CM07 bit in the CM0 register is set to 1 (sub clock) after the sub clock oscillation stabilizes, the sub

clock becomes the CPU clock source.

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

Figure 9.11

Sub Clock Circuit Connection

XCIN

XCOUT

Oscillator

CCIN

CCOUT

RCd(1)

MCU

(On-chip feedback resistor)

XCIN

XCOUT

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 XCIN and XCOUT following the instructions.

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