ST7LITE49M datasheet(65/188 Pages) STMICROELECTRONICS

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ST7LITE49M

Power saving modes

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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 wake-up event (reset or external interrupt).

9.5

Auto Wake Up from Halt mode

Auto Wake Up From Halt (AWUFH) mode is similar to Halt mode with the addition of a

specific internal RC oscillator for wake-up (Auto Wake-Up 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 realtime clock available.

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

Figure 31.

AWUFH mode block diagram

AWU RC

AWUFH

fAWU_RC

AWUFH

(ei0 source)

oscillator

prescaler/1 .. 255

interrupt

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divider

to 8-bit timer Input Capture

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