ST7LUS5 datasheet(47/124 Pages) STMICROELECTRONICS

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ST7LUS5, ST7LU05, ST7LU09

Power saving modes

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8.4.1

Active Halt mode

Active Halt mode is the lowest power consumption mode of the MCU with a real-time clock

available. It is entered by executing the ‘HALT’ instruction when active halt mode is enabled.

The MCU can exit Active Halt mode on reception of a Lite Timer / AT Timer interrupt or a

RESET.

●

When exiting Active Halt mode by means of a RESET, a 64 CPU cycle delay occurs.

After the start up delay, the CPU resumes operation by fetching the reset vector which

woke it up (see Figure 20).

●

When exiting Active Halt mode by means of an interrupt, the CPU immediately

resumes operation by servicing the interrupt vector which woke it up (see Figure 20).

When entering Active Halt mode, the I bit in the CC register is cleared to enable interrupts.

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

In Active Halt mode, only the main oscillator and the selected timer counter (LT/AT) are

running to keep a wake-up time base. All other peripherals are not clocked except those

which get their clock supply from another clock generator (such as external or auxiliary

oscillator).

Caution:

As soon as Active Halt is enabled, executing a HALT instruction while the Watchdog is active

does not generate a RESET if the WDGHALT bit is reset. This means that the device cannot

spend more than a defined delay in this power saving mode.

Figure 19.

Active Halt timing overview

This delay occurs only if the MCU exits Active Halt mode by means of a RESET.

HALT

RUN

64 CPU

CYCLE DELAY(1)

RESET

INTERRUPT

HALT

INSTRUCTION

FETCH

VECTOR

ACTIVE

[Active Halt Enabled]

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