ST7FOXA0 datasheet(48/123 Pages) STMICROELECTRONICS

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Power saving modes

ST7FOXA0

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Halt mode recommendations

●

Make sure that an external event is available to wake up the microcontroller from Halt

mode.

●

When using an external interrupt to wake up the microcontroller, reinitialize the

corresponding I/O as “Input Pull-up with Interrupt” before executing the HALT

instruction. The main reason for this is that the I/O may be wrongly configured due to

external interference or by an unforeseen logical condition.

●

For the same reason, reinitialize the level sensitiveness of each external interrupt as a

precautionary measure.

●

The opcode for the HALT instruction is 0x8E. To avoid an unexpected HALT instruction

due to a Program Counter failure, it is advised to clear all occurrences of the data value

0x8E from memory. For example, avoid defining a constant in ROM with the value

0x8E.

●

As the HALT instruction clears the I bit in the CC register to allow interrupts, the user

may choose to clear all pending interrupt bits before executing the HALT instruction.

This avoids entering other peripheral interrupt routines after executing the external

interrupt routine corresponding to the wakeup event (reset or external interrupt).

7.5

Auto wakeup from halt mode

Auto wakeup from halt (AWUFH) mode is similar to Halt mode with the addition of a specific

internal RC oscillator for wakeup (Auto wakeup from Halt oscillator) which replaces the main

clock which was active before entering Halt mode. Compared to Active-Halt mode, AWUFH

has lower power consumption (the main clock is not kept running), but there is no accurate

real-time clock available.

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

Figure 23.

AWUFH mode block diagram

AWU RC

AWUFH

fAWU_RC

AWUFH

(ei0 source)

oscillator

prescaler/1 .. 255

interrupt

/64

divider

to 8-bit timer Input Capture

Obsolete

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