UM10850
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© NXP B.V. 2016. All rights reserved.
User manual
Rev. 2.4 — 13 September 2016
222 of 464
NXP Semiconductors
UM10850
Chapter 15: LPC5410x Windowed Watchdog Timer (WWDT)
15.3 Basic configuration
The WWDT is configured through the following registers:
•
Power to the register interface (WWDT PCLK clock): set the WWDT bit in the
AHBCLKCTRL0 register,
•
For waking up from a WWDT interrupt, enable the watchdog interrupt for wake-up in
the STARTER0 register (
15.4 Pin description
The WWDT has no external pins.
15.5 General description
The purpose of the Watchdog Timer is to reset or interrupt the microcontroller within a
programmable time if it enters an erroneous state. When enabled, a watchdog reset is
generated if the user program fails to feed (reload) the Watchdog within a predetermined
amount of time.
When a watchdog window is programmed, an early watchdog feed is also treated as a
watchdog event. This allows preventing situations where a system failure may still feed
the watchdog. For example, application code could be stuck in an interrupt service that
contains a watchdog feed. Setting the window such that this would result in an early feed
will generate a watchdog event, allowing for system recovery.
The Watchdog consists of a fixed (divide by 4) pre-scaler and a 24-bit counter which
decrements when clocked. The minimum value from which the counter decrements is
0xFF. Setting a value lower than 0xFF causes 0xFF to be loaded in the counter. Hence the
minimum Watchdog interval is (T
WDCLK
256
4) and the maximum Watchdog interval is
(T
WDCLK
2
24
4) in multiples of (T
WDCLK
4). The Watchdog should be used in the
following manner:
•
Set the Watchdog timer constant reload value in the TC register.
•
Set the Watchdog timer operating mode in the MOD register.
•
Set a value for the watchdog window time in the WINDOW register if windowed
operation is desired.
Fig 33. WWDT timing
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