
Watchdog timer (WDG) ST72321xx-Auto
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10.5 Low power modes
10.6 Hardware watchdog option
If Hardware Watchdog is selected by option byte, the watchdog is always active and the
WDGA bit in the WDGCR is not used. Refer to the option byte description in Section 21.1.1:
Flash configuration on page 223.
10.7 Using Halt mode with the WDG (WDGHALT option)
The following recommendation applies if Halt mode is used when the watchdog is enabled:
Before executing the HALT instruction, refresh the WDG counter to avoid an unexpected
WDG reset immediately after waking up the microcontroller.
10.8 Interrupts
None.
Table 35. Effect of low power modes on WDG
Mode Effect
Slow No effect on Watchdog
Wait No effect on Watchdog
Halt
OIE bit in
MCCSR
register
WDGHALT
bit in
Option
Byte
00
No Watchdog reset is generated. The MCU enters Halt mode.
The Watchdog counter is decremented once and then stops
counting and is no longer able to generate a watchdog reset
until the MCU receives an external interrupt or a reset.
If an external interrupt is received, the Watchdog restarts
counting after 256 or 4096 CPU clocks. If a reset is generated,
the Watchdog is disabled (reset state) unless Hardware
Watchdog is selected by option byte. For application
recommendations see Section 10.7 below.
0 1 A reset is generated.
1x
No reset is generated. The MCU enters Active Halt mode. The
Watchdog counter is not decremented. It stop counting. When
the MCU receives an oscillator interrupt or external interrupt,
the Watchdog restarts counting immediately. When the MCU
receives a reset the Watchdog restarts counting after 256 or
4096 CPU clocks.
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