UM10429
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© NXP B.V. 2010. All rights reserved.
User manual
Rev. 1 — 20 October 2010
131 of 258
14.1 How to read this chapter
The WDT block is implemented on the LPC1102.
14.2 Basic configuration
The WDT is configured using the following registers:
1. Pins: The WDT uses no external pins.
2. Power: In the SYSAHBCLKCTRL register, set bit 15 (
3. Peripheral clock: Select the watchdog clock source
) and enable the WDT
peripheral clock by writing to the WDTCLKDIV register (
).
Remark:
The frequency of the watchdog oscillator is undefined after reset. The
watchdog oscillator frequency must be programmed by writing to the WDTOSCCTRL
register (see
) before using the watchdog oscillator as clock source for the
WDT.
14.3 Features
•
Internally resets chip if not periodically reloaded.
•
Debug mode.
•
Enabled by software but requires a hardware reset or a Watchdog reset/interrupt to be
disabled.
•
Incorrect/Incomplete feed sequence causes reset/interrupt if enabled.
•
Flag to indicate Watchdog reset.
•
Programmable 24 bit timer with internal pre-scaler.
•
Selectable time period from (T
WDCLK
×
256
×
4) to (T
WDCLK
×
2
24
×
4) in multiples of
T
WDCLK
×
4.
•
The Watchdog clock (WDCLK) source is selected in the syscon block from the
Internal RC oscillator (IRC), the main clock, or the Watchdog oscillator, see
This gives a wide range of potential timing choices for Watchdog operation under
different power reduction conditions. For increased reliability, it also provides the
ability to run the Watchdog timer from an entirely internal source that is not dependent
on an external crystal and its associated components and wiring.
14.4 Applications
The purpose of the Watchdog is to reset the microcontroller within a reasonable amount of
time if it enters an erroneous state. When enabled, the Watchdog will generate a system
reset if the user program fails to "feed" (or reload) the Watchdog within a predetermined
amount of time.
UM10429
Chapter 14: LPC1102 WatchDog Timer (WDT)
Rev. 1 — 20 October 2010
User manual