LPC1786 datasheet(59/117 Pages) NXP

59 / 117 page

LPC178X_7X

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Objective data sheet

Rev. 2 — 27 May 2011

59 of 117

NXP Semiconductors

LPC178x/7x

32-bit ARM Cortex-M3 microcontroller

7.30 Windowed WatchDog Timer (WWDT)

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

service it within a programmable time window.

7.30.1 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 is a dedicated watchdog oscillator, which is

always running if the watchdog timer is enabled.

7.31 RTC and backup registers

The RTC is a set of counters for measuring time when system power is on, and optionally

when it is off. The RTC on the LPC178x/7x is designed to have extremely low power

consumption, i.e. less than 1

A. The RTC will typically run from the main chip power

supply, conserving battery power while the rest of the device is powered up. When

operating from a battery, the RTC will continue working down to 2.1 V. Battery power can

be provided from a standard 3 V lithium button cell.

An ultra-low power 32 kHz oscillator will provide a 1 Hz clock to the time counting portion

of the RTC, moving most of the power consumption out of the time counting function.

The RTC includes a calibration mechanism to allow fine-tuning the count rate in a way

that will provide less than 1 second per day error when operated at a constant voltage and

temperature.

The RTC contains a small set of backup registers (20 bytes) for holding data while the

main part of the LPC178x/7x is powered off.

The RTC includes an alarm function that can wake up the LPC178x/7x from all reduced

power modes with a time resolution of 1 s.

7.31.1 Features

• Measures the passage of time to maintain a calendar and clock.

• Ultra low power design to support battery powered systems.

• Provides Seconds, Minutes, Hours, Day of Month, Month, Year, Day of Week, and

Day of Year.

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