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CHAPTER 6 LOW-POWER CONSUMPTION MODE
6.8 Precautions when Using Low-power Consumption Mode
6.8
Precautions when Using Low-power Consumption Mode
Special attention for the following is needed when using the low-power consumption
mode.
• Transition to standby mode and interrupt
• Cancellation of standby mode by interrupt
• Oscillation stabilization wait time
• Switching clock mode
• Notes on Accessing the Low-Power Consumption Mode Control Register (LPMCR) to
Enter the Standby Mode
■ Transition to Standby Mode and Interrupt
When there is the generation of an interrupt request to the CPU from the peripheral functions, the transition
to each standby mode is not made (the transition to the standby mode is not made even after the interrupt
processing) because even if you set "1" to the stop mode bit (STP) and the sleep mode bit (SLP) of the low-
power consumption mode control register (LPMCR), or "0" to the watch/time-base timer mode bit (TMD),
it is ignored. In this case, if the interrupt level is higher than 7, whether or not the interrupt request is
accepted by the CPU is not related to this operation.
Even when the CPU is currently performing interrupt processing, the device can go to the standby mode if
no other interrupt request is present with the interrupt request flag bit cleared.
■ Cancellation of Standby Mode by Interrupt
When an interrupt request with an interrupt level higher than 7 has been generated from a peripheral circuit,
etc. in sleep, time-base timer, or stop mode, standby mode is cleared. Whether or not the interrupt request is
accepted by the CPU is not related to this operation.
After the standby mode is canceled by the interruption, the operation is branched off to the interrupt
processing routine, if the priority of the interruption level set bit (IL2, IL1, IL0 bits of ICR register) to the
interrupt request is over the interrupt level mask register (ILM), and the interrupt is permitted by the I flag
of the condition cord register (CCR) (I=1). When an interrupt is not acceptable, processing from the
instruction succeeding the one which has specified standby mode continues.
When performing interrupt processing, interrupt processing normally transits after executing the instruction
succeeding the one specifying standby mode.
Depending on the conditions for transiting to standby mode, interrupt processing may starts before
executing the next instruction.
Note:
To prohibit a branch to the interrupt processing routine immediately after return, interrupts must be
prohibited before standby mode is set.
154
FUJITSU MICROELECTRONICS LIMITED
MB90335 Series
CM44-10137-6E
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