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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
1088 of 1441
37.1 How to read this chapter
The RTC is available on all LPC43xx/LPC43Sxx parts.
37.2 Basic configuration
The RTC is configured as follows:
•
See
for clocking and power control. The 1 kHz output of the 32 kHz
oscillator must be enabled in the CREG0 register in the CREG block (see
).
•
The RTC interrupt is connected to slot # 5 in the Event router slot #47 in the NVIC.
•
The functionality of the RTC_ALARM pin is controlled by the CREG0 register (see
). By default, the RTC Alarm interrupt can be monitored on this pin.
Remark:
After initializing the 32 kHz oscillator, wait for 2 sec before writing to the RTC
registers.
Remark:
Only write to the RTC registers while the 32 kHz oscillator is running. Repeated
writes to the RTC registers without the 32 kHz clock can stall the CPU. To confirm that the
32 kHz clock is running, read the Alarm timer counter register (DOWNCOUNTER, see
), which counts down from a preset value using the 1024 Hz clock signal derived
from the 32 kHz oscillator.
37.3 Features
•
Measures the passage of time to maintain a calendar and clock. Provides seconds,
minutes, hours, day of month, month, year, day of week, and day of year.
•
Ultra-low power design to support battery powered systems. Uses power from the
CPU power supply when it is present.
•
Dedicated battery power supply pin.
•
RTC power supply is isolated from the rest of the chip.
•
Calibration counter allows adjustment to better than
1 sec/day with 1 sec resolution.
•
Periodic interrupts can be generated from increments of any field of the time registers
and selected fractional second values.
•
An Alarm interrupt can be generated for a specific date/time.
UM10503
Chapter 37: LPC43xx/LPC43Sxx Real-Time Clock (RTC)
Rev. 2.1 — 10 December 2015
User manual
Table 874. RTC clocking and power control
Base clock
Branch clock Operating frequency
Clock to the RTC register
interface
BASE_M4_CLK
CLK_M4_BUS up to 204 MHz
32 kHz crystal oscillator output
for the RTC counter/timer clock
-
-
1024 Hz (fixed frequency);
the RTC receives an
internal 1 Hz clock.