LPC1111 datasheet(21/64 Pages) NXP

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LPC1111_12_13_14

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Product data sheet

Rev. 5 — 22 June 2011

21 of 64

NXP Semiconductors

LPC1111/12/13/14

32-bit ARM Cortex-M0 microcontroller

• Selectable time period from (Tcy(WDCLK)  256  4) to (Tcy(WDCLK)  224  4) in

multiples of Tcy(WDCLK)  4.

• The Watchdog Clock (WDCLK) source can be selected from the Internal RC oscillator

(IRC), the Watchdog oscillator, or the main clock. This gives a wide range of potential

timing choices of Watchdog operation under different power reduction conditions. It

also provides the ability to run the WDT from an entirely internal source that is not

dependent on an external crystal and its associated components and wiring for

increased reliability.

7.15 Windowed WatchDog Timer (LPC1100L series, LPC111x/102/202/302)

Remark: The windowed watchdog timer is available on parts LPC111x/102/202/302 .

The purpose of the watchdog is to reset the controller if software fails to periodically

service it within a programmable time window.

7.15.1 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 prior to

watchdog time-out.

• Enabled by software but requires a hardware reset or a watchdog reset/interrupt to be

disabled.

• 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 (Tcy(WDCLK)  256  4) to (Tcy(WDCLK)  224  4) in

multiples of Tcy(WDCLK)  4.

• The Watchdog Clock (WDCLK) source can be selected from the IRC or the dedicated

watchdog oscillator (WDO). This gives a wide range of potential timing choices of

watchdog operation under different power conditions.

7.16 Clocking and power control

7.16.1 Crystal oscillators

The LPC1111/12/13/14 include three independent oscillators. These are 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 LPC1111/12/13/14 will operate from the Internal RC oscillator until

switched by software. This allows systems to operate without any external crystal and the

bootloader code to operate at a known frequency.

See Figure 5 for an overview of the LPC1111/12/13/14 clock generation.

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