ST72361J4-Auto datasheet(67/279 Pages) STMICROELECTRONICS

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ST72361xx-Auto

Power saving modes

Doc ID 12468 Rev 3

67/279

It is entered by executing the HALT instruction when the AWUEN bit in the AWUCSR

Main clock controller with real time clock MCC/RTC for more details).

Figure 29.

AWUFH mode block diagram

As soon as HALT mode is entered, and if the AWUEN bit has been set in the AWUCSR

a fixed divider and a programmable prescaler controlled by the AWUPR register. The output

of this prescaler provides the delay time. When the delay has elapsed the AWUF flag is set

by hardware and an interrupt wakes up the MCU from Halt mode. At the same time the main

oscillator is immediately turned on and a 256 or 4096 cycle delay is used to stabilize it. After

this start-up delay, the CPU resumes operation by servicing the AWUFH interrupt. The AWU

flag and its associated interrupt are cleared by software reading the AWUCSR register.

To compensate for any frequency dispersion of the AWU RC oscillator, it can be calibrated

by measuring the clock frequency fAWU_RC and then calculating the right prescaler value.

Measurement mode is enabled by setting the AWUM bit in the AWUCSR register in Run

mode. This connects fAWU_RC to the ICAP1 input of the 16-bit timer, allowing the fAWU_RC to

be measured using the main oscillator clock as a reference time base.

Similarities with halt mode

The following AWUFH mode behavior is the same as normal Halt mode:

●

The MCU can exit AWUFH mode by means of any interrupt with exit from Halt

capability or a reset (see Section 7.4: Halt mode).

●

When entering AWUFH 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 AWUFH mode, the main oscillator is turned off causing all internal processing to be

stopped, including the operation of the on-chip peripherals. None of the peripherals are

clocked except those which get their clock supply from another clock generator (such

as an external or auxiliary oscillator like the AWU oscillator).

●

The compatibility of Watchdog operation with AWUFH mode is configured by the

WDGHALT option bit in the option byte. Depending on this setting, the HALT instruction

when executed while the Watchdog system is enabled, can generate a Watchdog

RESET.

AWU RC

AWUFH

fAWU_RC

AWUFH

(ei0 source)

oscillator

prescaler

interrupt

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divider

to Timer input capture

/1 .. 255

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