M32CSLASH86 datasheet(104/505 Pages) RENESAS

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Page 81

9. Clock Generation Circuit

)

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9.1.2 Sub Clock

Sub clock oscillation circuit generates the sub clock. The sub clock becomes clock source of the CPU

clock and for the timers A and B. The same frequency, fc, 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 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 XCIN

pin. Figure 9.10 shows an example of a sub clock circuit connection. Circuit constants vary depending on

each oscillator. Use the circuit constant recommended by each oscillator manufacturer.

The sub clock stops after reset. The feedback resistor is separated from the oscillation circuit. When the

PD8_6 and PD8_7 bits in the PD8 register are set to "0" (input mode) and the PU25 bit in the PUR2

function). The sub clock oscillation circuit starts oscillating. To apply an external clock to the XCIN pin, set

the CM04 bit to "1" when the PD8_7 bit is set to "0" and the PU25 bit to "0". The clock applied to the XCIN

pin becomes a clock source of the sub clock.

When the CM07 bit in the CM0 register is set to "1" (sub clock) after the sub clock oscillation has stabi-

lized, the sub clock becomes a CPU clock source.

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

details.

Figure 9.10 Sub Clock Circuit Connection

External Clock

XCIN

XCOUT

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 XCIN and XCOUT if the oscillator manufacturer recommends

placing the resistor externally.

Oscillator

RCd

(1)

CCIN

CCOUT

XCIN

XCOUT

Microcomputer

(Built-in Feedback Resistor)

Microcomputer

(Built-in Feedback Resistor)

VSS

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