M38047F2HKP datasheet(75/116 Pages) RENESAS

75 / 116 page

Rev.1.01

Jan 25, 2005

page 75 of 114

REJ03B0131-0101Z

3804 Group (Spec. H)

CLOCK GENERATING CIRCUIT

The 3804 group (Spec. H) has two built-in oscillation circuits: main

clock XIN-XOUT oscillation circuit and sub clock XCIN-XCOUT oscil-

lation circuit. An oscillation circuit can be formed by connecting a

resonator between XIN and XOUT (XCIN and XCOUT). Use the cir-

cuit constants in accordance with the resonator 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 external feed-back resistor is needed between XCIN

and XCOUT.

Immediately after power on, only the XIN oscillation circuit starts

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

Frequency Control

(1) Middle-speed mode

The internal clock

φ is the frequency of XIN divided by 8. After re-

set is released, this mode is selected.

(2) High-speed mode

The internal clock

φ is half the frequency of XIN.

(3) Low-speed mode

The internal clock

φ is half the frequency of XCIN.

(4) Low power dissipation mode

The low power consumption operation can be realized by stopping

the main clock XIN in low-speed mode. To stop the main clock, set

bit 5 of the CPU mode register to “1.” When the main clock XIN is

restarted (by setting the main clock stop bit to “0”), set sufficient

time for oscillation to stabilize.

Oscillation Control

(1) Stop mode

If the STP instruction is executed, the internal clock

φ stops at an

“H” level, and XIN and XCIN oscillators stop. When the oscillation

stabilizing time set after STP instruction released bit is “0,” the

prescaler 12 is set to “FF16” and timer 1 is set to “0116.” When the

oscillation stabilizing time set after STP instruction released bit is

“1,” set the sufficient time for oscillation of used oscillator to stabi-

lize since nothing is set to the prescaler 12 and timer 1.

After STP instruction is released, the input of the prescaler 12 is

connected to count source which had set at executing the STP in-

struction, and the output of the prescaler 12 is connected to timer

1. Set the timer 1 interrupt enable bit to disabled (“0”) before ex-

ecuting the STP instruction. Oscillator restarts when an external

interrupt is received, but the internal clock

φ is not supplied to the

CPU (remains at “H”) until timer 1 underflows. The internal clock

is supplied for the first time, when timer 1 underflows. Therefore

make sure not to set the timer 1 interrupt request bit to “1” before

the STP instruction stops the oscillator. When the oscillator is re-

started by reset, apply “L” level to the RESET pin until the

oscillation is stable since a wait time will not be generated.

The internal power supply circuit is changed to low power con-

sumption mode for consumption current reduction at the time of

STP instruction execution.

Although an internal power supply circuit is usually changed to the

normal operation mode at the time of the return from an STP in-

struction, since a certain time is required to start the power supply

to the flash memory and operation of flash memory to be enabled,

set wait time 100

µs or more by the oscillation stabilization time

set function after release of the STP instruction which used the

timer 1.

(2) Wait mode

If the WIT instruction is executed, the internal clock

φ stops at an

“H” level, but the oscillator does not stop. The internal clock

φ re-

starts when an interrupt is received. Since the oscillator does not

stop, normal operation can be started immediately after the clock

is restarted.

sNote

•If you switch the mode between middle/high-speed and low-

speed, stabilize both XIN and XCIN oscillations. The sufficient time

is required for the sub clock to stabilize, especially immediately

after power on and at returning from stop mode. When switching

the mode between middle/high-speed and low-speed, set the fre-

quency on condition that f(XIN) > 3f(XCIN).

•When using the quartz-crystal oscillator of high frequency, such

as 16 MHz etc., it may be necessary to select a specific oscillator

with the specification demanded.

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