UM10850
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User manual
Rev. 2.4 — 13 September 2016
232 of 464
NXP Semiconductors
UM10850
Chapter 16: LPC5410x Real-Time Clock (RTC)
16.4 General description
16.4.1 Real-time clock
The real-time clock is a 32-bit up-counter which can be cleared or initialized by software.
Once enabled, it counts continuously at a 1 Hz clock rate as long as the device is powered
up and the RTC remains enabled.
The main purpose of the RTC is to count seconds and generate an alarm interrupt to the
processor whenever the counter value equals the value programmed into the associated
32-bit match register.
If the part is in one of the reduced-power modes (deep-sleep, power-down, deep
power-down) an RTC alarm interrupt can also wake up the part to exit the power mode
and begin normal operation.
16.4.2 High-resolution/wake-up timer
The time interval required for many applications, including waking the part up from a
low-power mode, will often demand a greater degree of resolution than the one-second
minimum interval afforded by the main RTC counter. For these applications, a higher
frequency secondary timer has been provided.
This secondary timer is an independent, stand-alone wake-up or general-purpose timer
for timing intervals of up to 64 seconds with approximately one millisecond of resolution.
The High-Resolution/Wake-up Timer is a 16-bit down counter which is clocked at a 1 kHz
rate when it is enabled. Writing any non-zero value to this timer will automatically enable
the counter and launch a countdown sequence. When the counter is being used as a
wake-up timer, this write can occur just prior to entering a reduced power mode.
When a starting count value is loaded, the High-Resolution/Wake-up Timer will turn on,
count from the pre-loaded value down to zero, generate an interrupt and/or a wake-up
command, and then turn itself off until re-launched by a subsequent software write.
16.4.3 RTC power
The RTC module and the oscillator that drives it, run directly from device power pins. As a
result, the RTC will continue operating in deep power-down mode when power is
internally turned off to the rest of the device.
16.5 Pin description
gives a summary of pins related to the RTC.
Table 274. RTC pin description
Pin
Type
Description
RTCXIN
Input
RTC oscillator input.
RTCXOUT
Output
RTC oscillator output.