CD00001237 datasheet(45/105 Pages) STMICROELECTRONICS

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ST6215C ST6225C

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WATCHDOG TIMER (Cont’d)

These instructions test the C bit and reset the

MCU (i.e. disable the Watchdog) if the bit is set

(i.e. if the Watchdog is active), thus disabling the

Watchdog.

For more information on the use of the watchdog,

please read application note AN1015.

Note: This note applies only when the watchdog is

used as a standard timer. It is recommended to

read the counter twice, as it may sometimes return

an invalid value if the read is performed while the

counter is decremented (counter bits in transient

state). To validate the return value, both values

read must be equal. The counter decrements eve-

ry 384 µs at 8 MHz f

OSC.

9.1.5 Low Power Modes

9.1.6 Interrupts

None.

Mode

Description

WAIT

No effect on Watchdog.

STOP

Behaviour depends on the EXTCNTL option in the Option bytes:

1. Watchdog disabled:

The MCU will enter Stop mode if a STOP instruction is executed.

2. Watchdog enabled and EXTCNTL option disabled:

If a STOP instruction is encountered, it is interpreted as a WAIT.

3. Watchdog and EXTCNTL option enabled:

If a STOP instruction is encountered when the NMI pin is low, it is interpreted as a WAIT. If, however, the

STOP instruction is encountered when the NMI pin is high, the Watchdog counter is frozen and the CPU en-

ters STOP mode.

When the MCU exits STOP mode (i.e. when an interrupt is generated), the Watchdog resumes its activity.

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