Datasheet
UM10398 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2014. All rights reserved.
User manual Rev. 12.3 — 10 June 2014 399 of 547
23.1 How to read this chapter
The WDT block (not windowed) is available for parts LPC111x and LPC11Cxx.
For parts LPC11Cxx only, a clock source lock feature is implemented whenever the WDT
is enabled.
23.2 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 (Table 21
).
3. Peripheral clock: Select the watchdog clock source Table 25
) and enable the WDT
peripheral clock by writing to the WDTCLKDIV register (Table 27
).
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 Table 13
) before using the watchdog oscillator for the WDT.
4. Lock features: Once the watchdog timer is enabled by setting the WDEN bit in the
WDMOD register, the following lock features are in effect:
a. The WDEN bit cannot be changed to 0, that is the WDT cannot be disabled
(LPC111x/101/201/301 and LPC11Cxx).
b. The watch dog clock source cannot be changed. If the WDT is needed in
Deep-sleep mode, select the watch dog oscillator as the clock source before
setting the WDEN bit. (LPC11Cxx only).
23.3 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 Table 25
.
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.
UM10398
Chapter 23: LPC111x/LPC11Cxx WatchDog Timer (WDT)
Rev. 12.3 — 10 June 2014 User manual