38K2 datasheet(247/358 Pages) RENESAS

247 / 358 page

2.13 Standby function

Rev.2.00

Oct 15, 2006

page 98 of 112

38K2 Group

REJ09B0338-0200

APPLICATION

sRestoration by interrupt request

The occurrence of an interrupt request in the stop mode releases the stop mode. As a result,

oscillation is resumed. The interrupts available for restoration are:

•INT0, INT1

•CNTR0

•Serial I/O using an external clock

•Timer X using an external event count

•Key input (key-on wake-up)

•USB function (resume)

However, when using any of these interrupt requests for restoration from the stop mode, in order to

enable the selected interrupt, you must execute the STP instruction after setting the following conditions.

[Necessary register setting]

➀ Interrupt disable flag I = “0” (interrupt enabled)

➁ Timer 1 interrupt enable bit = “0” (interrupt disabled)

➂ Interrupt request bit of interrupt source to be used for restoration = “0” (no interrupt request

issued)

➃ Interrupt enable bit of interrupt source to be used for restoration = “1” (interrupts enabled)

For more details concerning interrupts, refer to “2.2 Interrupts”.

Oscillation is unstable when restarted. For this reason, time for stabilizing of oscillation (oscillation

stabilizing time) is required. For restoration by an interrupt request, waiting time prior to supplying

internal clock

φ to the CPU is automatically generated✽2 by Prescaler 12 and Timer 1✽1. This waiting

time is reserved as the oscillation stabilizing time on the system clock side. The supply of internal

clock

φ to the CPU is started at the Timer 1 underflow.

Figure 2.13.4 shows an execution sequence example at restoration by the occurrence of an INT0

interrupt request.

✽1: If the STP instruction is executed when the oscillation stabilizing time set after STP instruction

released bit is “0”, “FF16” and “0116” are automatically set in the Prescaler 12 counter/latch and

Timer 1 counter/latch, respectively. When the oscillation stabilizing time set after STP instruction

released bit is “1”, nothing is automatically set to either Prescaler 12 or Timer 1. For this reason,

any suitable value can be set to Prescaler 12 and Timer 1 for the oscillation stabilizing time.

✽2: Immediately after the oscillation is started, the count source is supplied to the prescaler 12 so

that a count operation is started.

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