Note For Transition To Standby Mode - Panasonic MN101L Series User Manual

4.2.4

Note for Transition to STANDBY Mode

While PSW.MIE is set to "1", if it can't be guaranteed that an interrupt for wakeup re-occurs after the transition to
STANBY mode since a maskable interrupt for wakeup has occurred before the transition to STANBY mode by
setting the CPUM register, CPU can not wake up from STANDBY mode.
Figure:4.2.13 shows the example that CPU can not wake up from STANDBY mode.
Therefore, it is necessary to prevent CPU from accepting a maskable interrupt for wakeup before the transition to
STANDBY mode.
To disable a maskable interrupt, set PSW.MIE to "0" before a maskable interrupt for wakeup occurs.
In addition, while CPUM.STOP or CPUM.HALT is set to "1", CPU returns to CPU operating mode by a
maskable interrupt for wakeup regardless of the value of PSW.MIE.
(The value of xICR.LV1-0 for an interrupt as a return factor needs to be smaller than the value of PSW.MIE.)
In this way, even if a maskable interrupt for wakeup occurs before the transition to STANDBY mode, CPU can
return to CPU operating mode by a maskable interrupt for wakeup since the interrupt is detected after the transi-
tion to STANDBY mode.
However, the interrupt processing is not executed because CPU just returns to CPU operating mode in this func-
tion. To execute the interrupt processing, it is necessary to set PSW.MIE to "1" after returning to CPU operating
mode.
Figure:4.2.14 shows the operation in STANDBY mode and the acceptance sequence of interrupt while an inter-
rupt is disabled.
When not executing the interrupt processing, it is necessary to set xICR.IR to "0" by software.
Figure:4.2.15 shows the operation in STANDBY mode and the non-acceptance sequence of interrupt while an
interrupt is disabled.
Return factor interrupt occured
Figure:4.2.13 Example of Not Returning to CPU Operating Mode
NORMAL/SLOW
mode
Enable maskable interrupts
Enable interrupt which
triggers return
Set HALT/STOP
mode
HALT/STOP
mode
CPU can't return the CPU operating mode,
because interrupt as the return factor is not occured again.
Set PSW.MIE to "1".
Set xICR.IE as the return factor.
Interrupt service routine
RTI
Watchdog timer
(
HLAT0/1/2/3 : conticue counting
STOP : stop counting
Chapter 4
Clock/ Mode/ Voltage Control
)
Mode Control Function IV - 23