UM10375 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
User manual Rev. 3 — 14 June 2011 304 of 368
19.1 How to read this chapter
This chapter describes the Windowed WDT available on the LPC1300L parts LPC1311/01
and LPC1313/01.
19.2 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 25
).
3. Peripheral clock: Select the WDT clock source (Table 34
) and enable the WDT
peripheral clock by writing to the WDTCLKDIV register (Table 36
).
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 15
) 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 cannot be disabled.
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.
19.3 Features
• Internally resets chip if not reloaded during the programmable time-out period.
• Optional windowed operation requires reload to occur between a minimum and
maximum time-out period, both programmable.
• Optional warning interrupt can be generated at a programmable time prior to
watchdog time-out.
• Programmable 24-bit timer with internal fixed pre-scaler.
• Selectable time period from 1,024 watchdog clocks (T
WDCLK
256 4) to over 67
million watchdog clocks (T
WDCLK
2
24
4) in increments of 4 watchdog clocks.
• “Safe” watchdog operation. Once enabled, requires a hardware reset or a Watchdog
reset to be disabled.
• A dedicated on-chip watchdog oscillator provides a reliable clock source that cannot
be turned off when the Watchdog Timer is running.
• Incorrect feed sequence causes immediate watchdog reset if the watchdog is
enabled.
• The watchdog reload value can optionally be protected such that it can only be
changed after the “warning interrupt” time is reached.
• Flag to indicate Watchdog reset.
UM10375
Chapter 19: LPC13xx Windowed WatchDog Timer (WWDT)
Rev. 3 — 14 June 2011 User manual
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