LPC64 datasheet(30/65 Pages) NXP

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LPC1768_67_66_65_64_3

Product data sheet

Rev. 03 — 19 November 2009

30 of 65

NXP Semiconductors

LPC1768/67/66/65/64

32-bit ARM Cortex-M3 microcontroller

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.

• Includes lock/safe feature.

7.28 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 LPC17xx is designed to have extremely low power

consumption, i.e. less than 1

μA. 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. A clock output function (see Section 7.29.4) makes measuring the oscillator

rate easy and accurate.

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

main part of the LPC17xx is powered off.

The RTC includes an alarm function that can wake up the LPC17xx from all reduced

power modes with a time resolution of 1 s.

7.28.1 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.

• Dedicated power supply pin can be connected to a battery or to the main 3.3 V.

• Periodic interrupts can be generated from increments of any field of the time registers.

• Backup registers (20 bytes) powered by VBAT.

• RTC power supply is isolated from the rest of the chip.

7.29 Clocking and power control

7.29.1 Crystal oscillators

The LPC17xx include three independent oscillators. These are the main oscillator, the IRC

oscillator, and the RTC oscillator. Each oscillator can be used for more than one purpose

as required in a particular application. Any of the three clock sources can be chosen by

software to drive the main PLL and ultimately the CPU.

Following reset, the LPC17xx 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.

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