ST62T45B STMicroelectronics, ST62T45B Datasheet - Page 23

• Manufacturer Part Number: ST62T45B
• Description: 8-BIT OTP/EPROM MCU
• Manufacturer: STMicroelectronics

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3.3 DIGITAL WATCHDOG
The digital Watchdog consists of a reloadable
downcounter timer which can be used to provide
controlled recovery from software upsets.
The Watchdog circuit generates a Reset when the
downcounter reaches zero. User software can
prevent this reset by reloading the counter, and
should therefore be written so that the counter is
regularly reloaded while the user program runs
correctly. In the event of a software mishap (usu-
ally caused by externally generated interference),
the user program will no longer behave in its usual
fashion and the timer register will thus not be re-
loaded periodically. Consequently the timer will
decrement down to 00h and reset the MCU. In or-
der to maximise the effectiveness of the Watch-
dog function, user software must be written with
this concept in mind.
Table 7. Recommended Option Choices
Functions Required
Stop Mode
Watchdog
Watchdog behaviour is governed by one option,
known as “WATCHDOG ACTIVATION” (i.e.
HARDWARE or SOFTWARE) (SeeTable 7).
In the SOFTWARE option, the Watchdog is disa-
bled until bit C of the DWDR register has been set.
When the Watchdog is disabled, low power Stop
mode is available. Once activated, the Watchdog
cannot be disabled, except by resetting the MCU.
In the HARDWARE option, the Watchdog is per-
manently enabled. Since the oscillator will run
continuously, low power mode is not available.
The STOP instruction is interpreted as a WAIT in-
struction, and the Watchdog continues to count-
down.
When the MCU exits STOP mode (i.e. when an in-
terrupt is generated), the Watchdog resumes its
activity.
“SOFTWARE WATCHDOG”
“HARDWARE WATCHDOG”
Recommended Optio ns
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