3886 datasheet(267/380 Pages) RENESAS

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3886 Group User’s Manual

APPLICATION

2.13 Standby function

2-150

Fig. 2.13.2 Execution sequence example at restoration by occurrence of INT0 interrupt request

(3)

Notes on using stop mode

sRestarting oscillation

Usually, when the MCU stops the clock oscillation by STP instruction and the STP instruction has

been released by an external interrupt source, the fixed values of Timer 1 and Prescaler 12 (Timer

1 = 0116, Prescaler 12 = FF16) are automatically reloaded in order for the oscillation to stabilize. The

user can inhibit the automatic setting by writing “1” to bit 6 of the port control register 2 (address

002F16).

However, by setting this bit to “1”, the previous values, set just before the STP instruction was

executed, will remain in Timer 1 and Prescaler 12. Therefore, you will need to set an appropriate

value to each register, in accordance with the oscillation stabilizing time, before executing the STP

instruction.

•Reason

Oscillation will restart when an external interrupt is received. However, internal clock phi is supplied

to the CPU only when Timer 1 underflows. This ensures time for the clock oscillation using the

ceramic resonators to be stabilized.

Stop mode

XIN or XCIN

(System clock)

INT0 pin

Prescaler 12 counter

Timer 1 counter

INT0 interrupt request bit

Peripheral device

CPU

Operating

Stopped

Operating

512 counts

Oscillation stabilizing time

XIN; “H”

XCIN; in high-impedance state

“FF16”

“0116”

Execute STP

instruction

INT0 interrupt signal

input (INT0 interrupt

request occurs)

Oscillation start

Prescaler 12 count start

512 counts down by

prescaler 12

Start supplying internal

clock

φ to CPU

Accept INT0 interrupt

request

Note: f(XIN)/16 or f(XCIN)/16 is input as the prescaler 12 count source.

qWhen restoring microcomputer from stop mode by INT0 interrupt (rising edge selected)

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