M38262EBFS datasheet(54/91 Pages) RENESAS

54 / 91 page

Rev.1.00

Sep 06, 2006

page 54 of 88

REJ03B0181-0100

3826 Group (One Time PROM version)

Fig. 59 Oscillator circuit

Fig. 60 External clock input circuit

CLOCK GENERATING CIRCUIT

The 3826 group has two built-in oscillation circuits: main clock

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

circuit. An oscillation circuit can be formed by connecting an oscil-

lator between XIN and XOUT (XCIN and XCOUT). Use the circuit

constants in accordance with the oscillator manufacturer’s recom-

mended values. 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 since a resistor does not exist between them.

To supply a clock signal externally, input it to the XIN pin and make

the XOUT pin open. The sub-clock oscillation circuit cannot directly

input clocks that are externally generated. Accordingly, be sure to

cause an external oscillator to oscillate.

Immediately after poweron, only the XIN oscillation circuit starts

oscillating, and XCIN and XCOUT pins go to high-impedance state.

Frequency Control

(1) Middle-speed mode

The clock input to the XIN pin is divided by 8 and it is used as the

system clock φ.

After reset, this mode is selected.

(2) High-speed mode

The clock input to the XIN pin is divided by 2 and it is used as the

system clock φ.

(3) Low-speed mode

•The clock input to the XCIN pin is divided by 2 and it is used as

the system clock φ.

•A low-power consumption operation can be realized by stopping

the main clock in this mode. To stop the main clock, set the main

clock stop bit of the CPU mode register to “1”.

When the main clock is restarted, after setting the main clock

stop bit to “0”, set enough time for oscillation to stabilize by pro-

gram.

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

speed, stabilize both XIN and XCIN oscillations. The suffi-

cient time is required for the sub clock to stabilize, espe-

cially immediately after poweron and at returning from stop

mode. When switching the mode between middle/high-

speed and low-speed, set the frequency in the condition

that f(XIN) > 3•f(XCIN).

Oscillation Control

(1) Stop mode

If the STP instruction is executed, the system clock φ stops at an

“H” level, and main and sub clock oscillators stop.

In this time, values set previously to timer 1 latch and timer 2 latch

are loaded automatically to timer 1 and timer 2. Before the STP

instruction, set the values to generate the wait time required for

oscillation stabilization to timer 1 latch and timer 2 latch (low-order

8 bits are set to timer 1, high-order 8 bits are set to timer 2). Either

f(XIN) or f(XCIN) divided by 16 is input to timer 1 as count source,

and the output of timer 1 is connected to timer 2.

The bits of the timer 123 mode register except bit 4 are set to “0”.

Set the timer 1 and timer 2 interrupt enable bits to “0” before ex-

ecuting the STP instruction.

Oscillation restarts at reset or when an external interrupt is re-

ceived, but the system clock φ is not supplied to the CPU until

timer 2 underflows. This allows time for the clock circuit oscillation

to stabilize when a ceramic resonator is used.

(2) Wait mode

If the WIT instruction is executed, only the system clock φ stops at

an “H” state. The states of main clock and sub clock are the same

as the state before the executing the WIT instruction, and oscilla-

tion does not stop. Since supply of internal clock φ is started im-

mediately after the interrupt is received, the instruction can be ex-

ecuted immediately.

XCIN

CIN

COUT

CCIN

CCOUT

XCOUT

XIN

XOUT

Notes :

Insert a damping resistor if required.

The resistance will vary depending on the oscillator and

the oscillation drive capacity setting.

Use the value recommended by the maker of the oscillator.

Also, if the oscillator manufacturer's data sheet specifies

that a feedback resistor be added external to the chip

though a feedback resistor exists on-chip, insert a feedback

resistor between XIN and XOUT following the instruction.

Rd (Note)

XIN

XOUT

External oscillation circuit

Open

VCC

VSS

CCIN

CCOUT

XCIN

XCOUT

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