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54.3.2 Configuring the Watchdog Once
All watchdog control bits, timeout value, and window value are write-once after
reset within 128 bus clocks. This means that after a write has occurred they cannot
be changed unless a reset occurs. This is guaranteed by the user configuring the
window and timeout value first, followed by the other control bits, and ensuring that
CS[UPDATE] is also set to 0.
This provides a robust mechanism to configure the watchdog and ensure that a runaway
condition cannot mistakenly disable or modify the watchdog configuration after
configured.
The new configuration takes effect only after all registers except CNT are written after
reset. Otherwise, the WDOG uses the reset values by default. If window mode is not used
(CS[WIN] is 0), writing to WIN is not required to make the new configuration take
effect.
54.3.2.1 Reconfiguring the Watchdog
In some cases (like when supporting a bootloader function), you may want to reconfigure
or disable the watchdog, without forcing a reset first.
• By setting CS[UPDATE] to 1 on the initial configuration of the watchdog after a
reset, you can reconfigure the watchdog at any time by executing an unlock
sequence.
• Conversely, if CS[UPDATE] remains 0, the only way to reconfigure the watchdog is
by initiating a reset.
The unlock sequence is similar to the refresh sequence but uses different values.
54.3.2.2 Unlocking the Watchdog
The unlock sequence can be the following:
• One 32-bit write of 0xD928_C520 to the CNT register
This should occur within 16 bus clocks at any time after the watchdog has been
configured. On completing the unlock sequence, the user must reconfigure the watchdog
within 128 bus clocks; otherwise, the watchdog closes the unlock window.
NOTE
Due to the 128 bus clocks requirement for reconfiguring the
watchdog, some delays must be inserted before executing
STOP or WAIT instructions after reconfiguring the watchdog.
This ensures that the watchdog's new configuration takes effect
Functional description
K32 L2A Reference Manual, Rev. 2, 01/2020
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NXP Semiconductors
Summary of Contents for K32 L2A Series
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