38D2 datasheet(60/136 Pages) RENESAS

60 / 136 page

Rev.3.02

Apr 10, 2008

Page 60 of 131

REJ03B0177-0302

38D2 Group

CLOCK GENERATING CIRCUIT

The oscillation circuit of 38D2 Group can be formed by

connecting an oscillator, capacitor and resistor between XIN and

XOUT (XCIN and XCOUT). To supply a clock signal externally,

input it to the XIN pin and make the XOUT pin open. The clocks

that are externally generated cannot be directly input to XCIN.

Use the circuit constants in accordance with the oscillator

manufacturer's recommended values. No external resistor is

needed between XIN and XOUT since a feed-back resistor exists

on-chip. (An external feed-back resistor may be needed

depending on conditions.) However, an about 10 M

Ω external

feedback resistor is needed between XCIN and XCOUT.

The 38D2 Group operation mode immediately after reset

depends on the OSCSEL pin state in the QzROM version.

When the OSCSEL pin state is GND level, the only on-chip

oscillator starts oscillating. The XIN-XOUT oscillation stops

oscillating, and XCIN and XCOUT pins function as I/O ports.

Flash memory version as same.

When the OSCSEL pin state is VCC level, the XIN-XOUT

oscillation divided by 8 starts oscillating. The on-chip oscillator

stops oscillating, and the XCIN and XCOUT pins function as I/O

ports.

Note the following in each mode.

•XIN Mode

The XIN-XOUT oscillation does not stop even if the XIN-XOUT

oscillation stop bit is set to “1”.

• Low-Speed Mode

The XCIN-XCOUT oscillation stops if the port XC switch bit is set

to “0”.

• On-Chip Oscillator Mode

Even if the on-chip oscillator stop bit is set to “1”, the on-chip

oscillator oscillation does not stop in the flash memory version,

but stops in the QzROM version.

• Frequency Control

(1) On-chip oscillation mode

The system clock

φ is the on-chip oscillator oscillation divided

by 32.

(2) XIN mode

Frequency/2 mode, frequency /4 mode, and frequency/8 mode

are collectively referred as XIN mode.

- Frequency/8 Mode

The system clock

φ is the frequency of XIN divided by 8.

- Frequency/4 Mode

The system clock

φ is the frequency of XIN divided by 4.

- Frequency/2 Mode

The system clock

φ is half the frequency of XIN.

(3)Low-speed Mode

The system clock

φ is half the frequency of sub clock.

After reset and when system returns from the stop mode, the

operation mode depends on the OSCSEL pin state in the

QzROM version and the flash memory version operation mode is

the on-chip oscillator mode.

When the RESET pin changes from “L” to “H” and when the

STP instruction is executed, determine the input level applied to

the OSCSEL pin.

Refer to the clock state transition diagram for the setting of

transition to each mode.

The XIN-OUT oscillation is controlled by the bit 5 of CPUM, and

the sub-clock oscillation is controlled by the bit 4 of CPUM and

the on-chip oscillator oscillation is controlled by the bit 0 of

CPUM2.

In the on-chip oscillator mode, the oscillation by the oscillator

can be stopped. In the low-speed mode, the power consumption

can be reduced by stopping the XIN

−XOUT oscillation.

In low-speed mode, the on-chip oscillator stops in the QzROM

version regardless of the on-chip oscillator stop bit value. The

on-chip oscillator does not stop in the flash memory version, so

set the on-chip oscillator stop bit to “1” to stop the oscillation.

Set enough time for oscillation to stabilize by programming to

restart the stopped oscillation and switch the operation mode.

Also, set enough time for oscillation to stabilize by programming

to switch the timer count source.

If you switch the mode between on-chip oscillator mode, XIN

mode and low-speed mode, stabilize both XIN and XCIN

oscillations. Especially be careful immediately after power-on

and at returning from stop mode. Refer to the clock state

transition diagram for the setting of transition to each mode. Set

the frequency in the condition that f(XIN) > 3

•f(XCIN).

When the XIN mode is not used (XIN-XOUT oscillation and

external clock input are not performed), connect XIN to VCC

through a resistor.

38D2 Datasheet(PDF) 60 Page - Renesas Technology Corp

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