ST10R272L - POWER REDUCTION MODES
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interrupt system is globally disabled) the CPU immediately resumes normal program
execution with the instruction following the IDLE instruction.
For a request programmed for PEC service, a PEC data transfer is performed if the priority
level of this request is higher than the current CPU priority, AND the interrupt system is
globally enabled. After the PEC data transfer has been completed, the CPU remains in Idle
Mode. Otherwise, if the PEC request cannot be serviced because low priority or a globally
disabled interrupt system, the CPU does not remain in Idle Mode but continues program
execution with the instruction following the IDLE instruction.
Idle Mode can also be terminated by a Non-Maskable Interrupt, i.e. a high to low transition
on the NMI pin. After Idle Mode has been terminated by an interrupt or NMI request, the
interrupt system performs a round of prioritization to determine the highest priority request.
In the case of an NMI request, the NMI trap will always be entered.
Any interrupt request whose individual Interrupt Enable flag is set before Idle Mode is
entered, terminates Idle Mode regardless of the current CPU priority. The CPU will not go
back into Idle Mode when a CPU interrupt request is detected, even when the interrupt was
not serviced because of a higher CPU priority or a globally disabled interrupt system
(IEN=’0’). The CPU will only go back into Idle Mode when the interrupt system is globally
enabled (IEN=’1’) and a PEC service on a priority level higher than the current CPU level is
requested and executed.
Note
An interrupt request which is individually enabled and assigned to priority level 0
will terminate Idle Mode. However, he associated interrupt vector will not be
accessed.
The Watchdog Timer can monitor Idle Mode: an internal reset is generated if no interrupt or
NMI request occurs before the Watchdog Timer overflows. To prevent Watchdog Timer
overflow during Idle Mode, it must be programmed with a reasonable time interval - before
Idle Mode is entered.
Figure 116 Transitions between Idle Mode and active mode
Active
Mode
Idle
Mode
IDLE instruction
CPU Interrupt Request
Denied PEC Request
Executed
PEC Request
denied
accepted