STR720 datasheet(73/401 Pages) STMICROELECTRONICS

73 / 401 page

STR720 - WAKE-UP INTERRUPT UNIT (WIU)

73/401

8.3.3

STOP Mode Entering Conditions

Assuming the device is in Run mode, during the STOP bit setting sequence the following case

may occur:

Case 1: A wake-up event on the external wake-up lines occurs during the STOP bit

setting sequence

There are two possible cases:

Interrupt requests to the CPU are disabled: in this case the device will not enter STOP

mode, no interrupt service routine will be executed and the program execution continues

from the instruction following the STOP bit setting sequence. The status of STOP bit will

be again:

STOP = 0

The application can determine why the device did not enter STOP mode by polling the

pending bits of the external lines (at least one must be at 1).

Interrupt requests to CPU are enabled: in this case the device will not enter STOP mode

and the interrupt service routine will be executed. The status of STOP bit will be again:

STOP = 0

The interrupt service routine can determine why the device did not enter STOP mode by

polling the pending bits of external lines (at least one must be at 1).

Case 2: wrong STOP bit setting sequence

This can happen if an Interrupt request is acknowledged during the STOP bit setting

sequence. In this case polling on STOP bit (WUCTRL register) will give:

STOP = 0

This means that device did not enter STOP mode due to a bad STOP bit setting sequence:

the user shall retry the entire sequence.

Case 3: correct STOP bit setting sequence

In this case the device enters STOP mode.

The WKUP-INT bit can be used by an interrupt routine to detect and to distinguish events

coming from Interrupt Mode or from Wake-up Mode, allowing the code to execute different

procedures.

To exit STOP mode, it is sufficient that one of the 16 wake-up lines (not masked) generates an

event: the clock restarts after the delay needed for the oscillator to restart.

Note: After exiting from STOP Mode, the software can successfully reset the pending bits

(edge sensitive), even though the corresponding wake-up line is still active (high or low,

depending on the Trigger Event register programming); the user must poll the external pin

status to detect and distinguish a short event from a long one (for example a different key

pushing time).

STR720 датащи(PDF) 73 Page - STMicroelectronics