RM0312 datasheet(71/275 Pages) STMICROELECTRONICS

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RM0312

Power management

9.4.2

Halt mode

In this mode the master clock is stopped. This means that the CPU and all the peripherals

clocked by fMASTER or by derived clocks are disabled. As a result, none of the peripherals

are clocked and the digital part of the MCU consumes almost no power.

The Main Voltage Regulator (MVR) is switched off automatically when the MCU enters Halt

mode. The MCU core is powered only by the Low Power Voltage Regulator (LPVR) and all

the registers and RAM contents are preserved.

The MCU enters Halt mode when a HALT instruction is executed. Wakeup from Halt mode

is triggered by an external interrupt, sourced by a general purpose I/O port configured as

interrupt input or by an alternate function pin capable of triggering a peripheral interrupt.

In an interrupt based application, where most of the processing is done through the interrupt

routines, the main program may be suspended by setting the activation level bit (AL) in the

CPU configuration register. Setting this bit causes the CPU to return to Halt mode when

executing the return from interrupt, without restoring the main execution context.

This saves power by removing the save/restore context activity and by removing the need to

execute a main level software loop for power management (in order to return to WFI mode).

Caution:

Before entering Halt mode, the ProxSense peripheral must be disabled or in Low power

mode (PXS_EN = ‘0’ or LOW_POWER = ‘1’ in register PXS_CR1).

9.4.3

Active-halt mode

Active-halt mode is similar to Halt mode except that it does not require an external interrupt

for wake up. It uses the AWU to generate a wakeup event internally after a programmable

delay or the PXS to generate a wakeup event after a PXS interrupt occurrence.

Active-halt mode with AWU

To enter Active-halt mode with AWU, first enable the AWU as described in the AWU section.

Then execute a HALT instruction.

In Active-halt mode with AWU, the main oscillator, the CPU and almost all peripherals are

stopped. Only the LSI RC oscillator is running to drive the AWU counters, BEEP and IWDG

counter if enabled.

The Main Voltage Regulator (MVR) is switched off automatically when the MCU enters

Active-halt mode. The MCU core is powered only by the Low Power Voltage Regulator

(LPVR) and all registers and RAM contents are preserved.

In order to reduce the consumption when using the Active-halt mode with AWU, the

ProxSense must be disabled (PXS_EN = ‘0’ in register PXS_CR1) or in Low power mode

(LOW_POWER = ‘1’ in register PXS_CR1).

Active-halt mode with ProxSense

To enter Active-halt mode with ProxSense, an acquisition must be in progress (CIPF = ‘1’ in

not enter Active-halt mode with ProxSense if the synchronization trigger does not occur

before the Halt instruction execution. This can be checked by polling the CIPF bit in the

PXS_ISR register.

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