Nxp Semiconductors OM11043 Data Sheet
LPC1769_68_67_66_65_64_63
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Product data sheet
Rev. 9.5 — 24 June 2014
36 of 89
NXP Semiconductors
LPC1769/68/67/66/65/64/63
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.
that is not dependent on an external crystal and its associated components and wiring
for increased reliability.
•
Includes lock/safe feature.
8.28 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
when it is off. The RTC on the LPC17xx 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.
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.
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
that will provide less than 1 second per day error when operated at a constant voltage and
temperature. A clock output function (see
) 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.
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.
power modes with a time resolution of 1 s.
8.28.1 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.
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.
8.29 Clocking and power control
8.29.1 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.
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.
software. This allows systems to operate without any external crystal and the bootloader
code to operate at a known frequency.