Datasheet
LPC11E3X All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 2.3 — 11 September 2014 25 of 71
NXP Semiconductors
LPC11E3x
32-bit ARM Cortex-M0 microcontroller
7.15 System tick timer
The ARM Cortex-M0 includes a system tick timer (SYSTICK) that is intended to generate
a dedicated SYSTICK exception at a fixed time interval (typically 10 ms).
7.16 Windowed WatchDog Timer (WWDT)
The purpose of the WWDT is to prevent an unresponsive system state. If software fails to
update the watchdog within a programmable time window, the watchdog resets the
microcontroller
7.16.1 Features
• Internally resets chip if not periodically reloaded during the programmable time-out
period.
• Optional windowed operation requires reload to occur between a minimum and
maximum time period, both programmable.
• Optional warning interrupt can be generated at a programmable time before watchdog
time-out.
• Software enables the WWDT, but a hardware reset or a watchdog reset/interrupt is
required to disable the WWDT.
• Incorrect feed sequence causes reset or interrupt, if enabled.
• Flag to indicate watchdog reset.
• Programmable 24-bit timer with internal prescaler.
• Selectable time period from (T
cy(WDCLK)
256 4) to (T
cy(WDCLK)
2
24
4) in
multiples of T
cy(WDCLK)
4.
• The Watchdog Clock (WDCLK) source can be selected from the IRC or the dedicated
watchdog oscillator (WDO). The clock source selection provides a wide range of
potential timing choices of watchdog operation under different power conditions.
7.17 Clocking and power control
7.17.1 Integrated oscillators
The LPC11E3x include three independent oscillators: the system oscillator, the Internal
RC oscillator (IRC), and the watchdog oscillator. Each oscillator can be used for more
than one purpose as required in a particular application.
Following reset, the LPC11E3x operates from the internal RC oscillator until software
switches to a different clock source. The IRC allows the system to operate without any
external crystal and the bootloader code to operate at a known frequency.
See Figure 7
for an overview of the LPC11E3x clock generation.