3886 datasheet(59/111 Pages) RENESAS

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3886 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS

CLOCK GENERATING CIRCUIT

The 3886 group has two built-in oscillation circuits. An oscillation

circuit can be formed by connecting a resonator between XIN and

XOUT (XCIN and XCOUT). Use the circuit constants in accordance

with the resonator manufacturer’s recommended values. No exter-

nal resistor is needed between XIN and XOUT since a feed-back

resistor exists on-chip. 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, 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.

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 af-

ter 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).

(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.

Either XIN or XCIN divided by 16 is input to the prescaler 12 as

count source, and the output of the prescaler 12 is connected to

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

executing 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.

(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 at reset or when an interrupt is received. Since the oscillator

does not stop, normal operation can be started immediately after

the clock is restarted.

Fig. 58 Ceramic resonator circuit

Fig. 59 External clock input circuit

XCIN

XCOUT

XIN

XOUT

CIN

COUT

CCIN

CCOUT

VCC

VSS

XCIN

XCOUT

XIN

XOUT

Open

External oscillation

circuit

External oscillation

circuit

VCC

VSS

3886 Datasheet(PDF) 59 Page - Renesas Technology Corp

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