
CHAPTER 21 STANDBY FUNCTION
User
’
s Manual U15862EJ3V0UD
661
21.3 IDLE Mode
21.3.1 Setting and operation status
The IDLE mode is set by clearing the PSM bit of the power save mode register (PSMR) to 0 and setting the STP bit
of the power save control register (PSC) to 1 in the normal operation mode.
In the IDLE mode, the clock oscillator continues operation but clock supply to the CPU and other on-chip peripheral
functions stops.
As a result, program execution stops and the contents of the internal RAM before the IDLE mode was set are
retained. The CPU and other on-chip peripheral functions stop operating. However, the on-chip peripheral functions
that can operate with the subclock or an external clock continue operating.
Table 21-5 shows the operation status in the IDLE mode.
The IDLE mode can reduce the current consumption more than the HALT mode because it stops the operation of
the on-chip peripheral functions. The main clock oscillator does not stop, so the normal operation mode can be
restored without waiting for the oscillation stabilization time after the IDLE mode has been released, in the same
manner as when the HALT mode is released.
Caution
Insert five or more NOP instructions after the instruction that stores data in the PSC register to
set the IDLE mode.
21.3.2 Releasing IDLE mode
The IDLE mode is released by a non-maskable interrupt request (NMI pin input), unmasked external interrupt
request (INTP0 to INTP6 pin input), unmasked internal interrupt request from the peripheral functions operable in the
IDLE mode, or RESET input.
After the IDLE mode has been released, the normal operation mode is restored.
(1) Releasing IDLE mode by non-maskable interrupt request or unmasked maskable interrupt request
The IDLE mode is released by a non-maskable interrupt request or an unmasked maskable interrupt request,
regardless of the priority of the interrupt request. If the IDLE mode is set in an interrupt servicing routine,
however, an interrupt request that is issued later is processed as follows.
(a) If an interrupt request with a priority lower than that of the interrupt request currently being serviced is
issued, only the IDLE mode is released, and that interrupt request is not acknowledged. The interrupt
request itself is retained.
(b) If an interrupt request with a priority higher than that of the interrupt request currently being serviced is
issued (including a non-maskable interrupt request), the IDLE mode is released and that interrupt request
is acknowledged.
Table 21-4. Operation After Releasing IDLE Mode by Interrupt Request
Release Source
Interrupt Enabled (EI) Status
Interrupt Disabled (DI) Status
Non-maskable interrupt request
Execution branches to the handler address
Maskable interrupt request
Execution branches to the handler
address or the next instruction is
executed
The next instruction is executed