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ST92141 - INTERRUPTS

WAKE-UP / INTERRUPT LINES MANAGEMENT UNIT (Cont’d)

2. Interrupt requests to CPU are enabled: in this

case the ST9 will not enter STOP mode and the

interrupt service routine will be executed. The

status of STOP and EX_STP bits will be again:

STOP = 0, EX_STP = 0

The interrupt service routine can determine why

the ST9 did not enter STOP mode by polling

the pending bits of the external lines (at least

one must be at 1).

If the MCU really exits from STOP Mode, the

RCCU EX_STP bit is still set and must be reset by

software. Otherwise, if an Interrupt/DMA request

was acknowledged during the STOP bit setting se-

quence, the RCCU EX_STP bit is reset. This

means that the MCU has filtered the STOP Mode

entry request.

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, allow-

ing 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 sen-

sitive), 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 dis-

tinguish a short event from a long one (for example

keyboard input with keystrokes of varying length).

3.12.4 Programming Considerations

The following paragraphs give some guidelines for

designing an application program.

3.12.4.1 Procedure for Entering/Exiting STOP

mode

1. Program the polarity of the trigger event of

external wake-up lines by writing registers

WUTRH and WUTRL.

2. Check that at least one mask bit (registers

WUMRH, WUMRL) is equal to 1 (so at least

one external wake-up line is not masked).

3. Reset at least the unmasked pending bits: this

allows a rising edge to be generated on the

INTD1 channel when the trigger event occurs

(an interrupt on channel INTD1 is recognized

when a rising edge occurs).

4. Select the interrupt source of the INTD1 chan-

nel (see description of ID1S bit in the WUCTRL

5. To generate an interrupt on channel INTD1, bits

EITR.1 (R242.7, Page 0) and EIMR.1 (R244.7,

Page 0) must be set and bit EIPR.7 must be

reset. Bits 7 and 6 of register R245, Page 0

must be written with the desired priority level for

interrupt channel INTD1.

6. Reset the STOP bit in register WUCTRL and

the EX_STP bit in the CLK_FLAG register

(R242.7, Page 55). Refer to the RCCU chapter.

7. To enter STOP mode, write the sequence 1, 0,

1 to the STOP bit in the WUCTRL register with

three consecutive write operations.

8. The code to be executed just after the STOP

sequence must check the status of the STOP

and RCCU EX_STP bits to determine if the ST9

entered STOP mode or not (See “Wake-up

Mode Selection” on page 56. for details). If the

ST9 did not enter in STOP mode it is necessary

to reloop the procedure from the beginning, oth-

erwise the procedure continues from next point.

9. 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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