STR720 datasheet(79/401 Pages) STMICROELECTRONICS

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STR720 - WAKE-UP INTERRUPT UNIT (WIU)

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8.6 Programming considerations

The following paragraphs give some guidelines for the design of the application program.

8.6.1

Procedure for Entering/Exiting STOP mode

Program the polarity of the trigger event of external wake-up lines by writing register

WUTR.

Check that at least one mask bit (register WUMR) is equal to 1 (at least one external

wake-up line is not masked).

Reset at least the unmasked pending bits: this allows to generate a rising edge on the

Interrupt channel WUI_INT when the trigger event occurs (an interrupt is recognized

when a rising edge occurs).

Select the interrupt source of the channel (see description of INT_EN bit in the WUCTRL

Note

If clock line is chosen as wake-up event, it should be considered that as long as

clock source is active the corresponding pending bit will be seen at ‘1’.

Note

The change of PLL lock condition cannot be used as wake-up event. Selecting this

input as the only wake-up source will stuck the system so as only a reset event can

restore normal operations.

To generate an interrupt on the associated channel, set the related enable, mask and

priority bits in the interrupt controller.

Reset the STOP bit in register WUCTRL.

To enter STOP mode, write the sequence 1, 0, 1 on the STOP bit in the WUCTRL register

with three write operations. To reset the sequence it is sufficient to write twice a logic ‘0’ to

the STOP bit of WUCTRL register (corresponding anyway to a bad sequence). If the

sequence is not completed within 64 clock periods (system clock), a TIMEOUT expires

and reset the sequence. In this case the software shall re-enter the sequence (1, 0,1).

The code to be executed just after the STOP sequence must check the STOP bit status to

determine if the device entered STOP mode or not (See “Wake-up Mode Selection” on

page 72. for details). If the device did not enter in STOP mode it is necessary to re-loop

the procedure from the beginning, otherwise the procedure continues from next point (see

also section 25.4 on page 368).

Poll the wake-up pending bits to determine which wake-up line caused the exit from STOP

mode.

10 Clear the wake-up pending bit that was set.

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