UM10503
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
927 of 1269
NXP Semiconductors
UM10503
Chapter 35: LPC43xx Real-Time Clock (RTC)
35.4 General description
The Real Time Clock (RTC) is a set of counters for measuring time when system power is
on, and optionally when it is off. It uses very little power when its registers are not being
accessed by the CPU, especially in reduced power modes. On the LPC43xx, the RTC is
clocked by a separate 32 kHz oscillator that produces a 1 Hz internal time reference. The
RTC is powered by its own power supply pin, VBAT.
35.5 Pin description
Fig 112. RTC functional block diagram
day of
year
second
minute
hour
day
month
year
alarm compare
second
minute
hour
day
month
year
day of
week
calibration counter
calibration compare register
calibration
control
logic
calibration compare
sign
bit
match
counter
reset
LSB
set
LSB
out
Time Registers
Alarm Registers
Calibration
Alarm out
and Alarm
Interrupts
Counter
Increment
Interrupts
1 Hz
Clock
Table 781. RTC pin description
Pin function
Direction
Description
RTC_ALARM
O
RTC controlled output. This is a 1.8 V pin. The pin goes
HIGH when an RTC alarm is generated. CREG0 bits
ALARMCTRL must be set to 0
(see