3886 Group User’s Manual
APPLICATION
2-149
2.13 Standby function
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–INT4
CNTR0, CNTR1
Serial I/O (1, 2) using an external clock
Timer X, Y using an external event count
Key input (key-on wake-up)
Bus interface
SCL/SDA
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]
Interrupt disable flag I = “0” (interrupt enabled)
Timer 1 interrupt enable bit = “0” (interrupt disabled)
Interrupt request bit of interrupt source to be used for restoration = “0” (no interrupt request
issued)
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 generated2 by Prescaler 12 and Timer 11. 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 2.13.2 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.