ST72321R7-Auto datasheet(67/243 Pages) STMICROELECTRONICS

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ST72321xx-Auto

Power saving modes

Doc ID 13829 Rev 1

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8.4.2

Halt mode

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

executing the ‘HALT’ instruction when the OIE bit of the Main Clock Controller Status

beeper (MCC/RTC) on page 82 for more details on the MCCSR register).

The MCU can exit Halt mode on reception of either a specific interrupt (see Section Table

20.: Interrupt mapping on page 56) 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 start up delay, the CPU resumes

operation by servicing the interrupt or by fetching the reset vector which woke it up (see

Figure 28).

When entering Halt mode, the I[1:0] bits in the CC register are forced to ‘10b’ 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

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

auxiliary oscillator).

The compatibility of Watchdog operation with Halt mode is configured by the ‘WDGHALT’

option bit of the option byte. The HALT instruction when executed while the Watchdog

system is enabled, can generate a Watchdog RESET (see Section 21.1.1: Flash

configuration on page 223 for more details).

Figure 27.

Halt timing overview

HALT

RUN

256 OR 4096 CPU

CYCLE DELAY

RESET

INTERRUPT

HALT

INSTRUCTION

FETCH

VECTOR

[MCCSR.OIE = 0]

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