Precautions At Using Low-Power Consumption Mode - Fujitsu MB90420/5 (A) Series Hardware Manual

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MB90420/5 (A) SERIES F MC-16LX FAMILY 16-BIT MICROCONTROLLERS HARDWARE MANUAL

5.8 Precautions at Using Low-power Consumption Mode

Precautions at using the low-power consumption mode are shown below.
• Transition to standby mode and interrupt
• Cancellation of standby mode by interrupt
• At cancellation of stop mode
• Oscillation stabilization wait time
n Transition to standby mode and interrupt
When an interrupt request is already issued from the resource function to the CPU, low-power consumption
mode (LPMCR: STP = 1, SLP = 1) or (LPMCR: TMD = 0) are ignored, so no transition is performed to each
standby mode (Even after interrupt handling, no transition is performed to each standby mode). This
operation is performed irrespective of whether the interrupt request is accepted by the CPU, when the
interrupt request with an interrupt level is higher than 7.
Also, even when the CPU is under interrupt handling, a transition can be performed to the standby mode
when the interrupt request flag bit is cleared and no other interrupt request is issued.
n Cancellation of standby mode by interrupt
The standby mode is cancelled when an interrupt request with an interrupt level higher than 7 is issued from
the resource during the sleep mode, time-base timer mode, or stop mode. This operation is performed
irrespective of whether the interrupt request is accepted by the CPU.
After cancellation of standby mode, a branch is caused to the interrupt-processing routine as an normal
interrupt processing under the following conditions: the priority specified for the interrupt level setting bits
(ICR: IL2, IL1, IL0) corresponding to the interrupt request is higher than the interrupt level mask register
(ILM), and the interrupt enable flag of the condition code register is enabled (CCR: I = 1). When the
interrupt is not accepted by the CPU, operation is resumed at the instruction immediately after the one that
specified the standby mode.
At interrupt handling, normally the instruction immediately after the one that specifies the standby mode is
executed, and then interrupt handling is performed. However, depending on the condition at the transition to
the standby mode, interrupt handling may be performed before executing the next instruction.
When not causing a branch to the interrupt processing routine immediately after a return, take measures
such as disabling the interrupt before setting the standby mode.
n At cancellation of stop mode
Before entering the stop mode, it can be cancelled by an input according to the setting of the interrupt input
factor for the external interrupt.
The interrupt input factor can be selected from H level, L level, rising edge, and falling edge.
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