LPC178X datasheet(59/120 Pages) NXP

59 / 120 page

LPC178X_7X

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Preliminary data sheet

Rev. 4 — 1 May 2012

59 of 120

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 very low power

consumption. 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 provides 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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