
UM10800
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© NXP Semiconductors N.V. 2016. All rights reserved.
User manual
Rev. 1.2 — 5 October 2016
300 of 487
NXP Semiconductors
UM10800
Chapter 17: LPC82x Windowed Watchdog Timer (WWDT)
17.5.3 Using the WWDT lock features
The WWDT supports several lock features which can be enabled to ensure that the
WWDT is running at all times:
•
Disabling the WWDT clock source
•
Changing the WWDT reload value
17.5.3.1 Disabling the WWDT clock source
If bit 5 in the WWDT MOD register is set, the WWDT clock source is locked and can not
be disabled either by software or by hardware when Sleep, Deep-sleep or Power-down
modes are entered. Therefore, the user must ensure that the watchdog oscillator for each
power mode is enabled
before
setting bit 5 in the MOD register.
In Deep power-down mode, no clock locking mechanism is in effect because no clocks
are running. However, an additional lock bit in the PMU can be set to prevent the part from
even entering Deep power-down mode (see
).
17.5.3.2 Changing the WWDT reload value
If bit 4 is set in the WWDT MOD register, the watchdog time-out value (TC) can be
changed only after the counter is below the value of WDWARNINT and WDWINDOW.
The reload overwrite lock mechanism can only be disabled by a reset of any type.