ST7LITE25F2 datasheet(54/166 Pages) STMICROELECTRONICS

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Power saving modes

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Doc ID 8349 Rev 5

Figure 23. WAIT mode flowchart

Before servicing an interrupt, the CC register is pushed on the stack. The I bit of the CC register is set

during the interrupt routine and cleared when the CC register is popped.

9.4

HALT mode

The HALT mode is the lowest power consumption mode of the MCU. It is entered by

executing the "HALT” instruction when ACTIVVE-HALT is disabled (see Section 9.5:

ACTIVE-HALT mode for more details) and when the AWUEN bit in the AWUCSR register is

cleared.

The MCU can exit HALT mode on reception of either a specific interrupt (see Table 12:

Interrupt mapping) or a reset. When exiting HALT mode by means of a reset or an interrupt,

the oscillator is immediately turned on and the 256 or 4096 CPU cycle delay is used to

stabilize the oscillator. After the startup delay, the CPU resumes operation by servicing the

interrupt or by fetching the reset vector which woke it up (see Figure 25: HALT mode

flowchart).

When entering HALT mode, the I bit in the CC register is forced to 0 to enable interrupts.

Therefore, if an interrupt is pending, the MCU wakes up immediately.

In HALT mode, the main oscillator is turned off causing all internal processing to be stopped,

including the operation of the on-chip peripherals. All peripherals are not clocked except the

WFI INSTRUCTION

RESET

INTERRUPT

CPU

OSCILLATOR

PERIPHERALS

IBIT

OFF

Fetch reset vector

or service interrupt

CPU

OSCILLATOR

PERIPHERALS

IBIT

OFF

CPU

OSCILLATOR

PERIPHERALS

IBIT

X(1)

cycle delay

256 or 4096 CPU clock

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