
CHAPTER 21 STANDBY FUNCTION
User
’
s Manual U15862EJ3V0UD
663
21.4 STOP Mode
21.4.1 Setting and operation status
The STOP mode is set when the PSM bit of the power save mode register (PSMR) is set to 1 and the STP bit of
the power save control register (PSC) is set to 1 in the normal operation mode.
In the STOP mode, the subclock oscillator continues operating but the main clock oscillator stops. Clock supply to
the CPU and the on-chip peripheral functions is stopped.
As a result, program execution is stopped, and the contents of the internal RAM before the STOP mode was set
are retained. The on-chip peripheral functions that operate with the clock oscillated by the subclock oscillator or an
external clock continue operating.
Table 21-7 shows the operation status in the STOP mode.
Because the STOP stops operation of the main clock oscillator, it reduces the current consumption to a level lower
than the IDLE mode. If the subclock oscillator and external clock are not used, the power consumption can be
minimized with only leakage current flowing.
Caution
Insert five or more NOP instructions after the instruction that stores data in the PSC register to
set the STOP mode.
21.4.2 Releasing STOP mode
The STOP 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
STOP mode, or RESET pin input.
After the STOP mode has been released, the normal operation mode is restored after the oscillation stabilization
time has been secured.
(1) Releasing STOP mode by non-maskable interrupt request or unmasked maskable interrupt request
The STOP 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 software STOP mode is set in an interrupt servicing
routine, however, an interrupt request that is issued later is serviced as follows.
(a) If an interrupt request with a priority lower than that of the interrupt request currently being serviced is
issued, only the STOP 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 STOP mode is released and that interrupt
request is acknowledged.
Table 21-6. Operation After Releasing STOP 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