UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
423 of 515
23.1 How to read this chapter
The self-wake-up timer is available on all LPC84x parts.
23.2 Features
•
32-bit, loadable down counter. Counter starts automatically when a count value is
loaded. Time-out generates an interrupt/wake up request.
•
The WKT resides in a separate, always-on power domain.
•
The WKT supports three clock sources: The FRO, the internal low-power oscillator, or
the WKTCLKIN pin. The low-power oscillator and the external clock are valid clock
sources in all power modes including deep power-down. The FRO can be used in
sleep and active mode only.
•
Depending on the clock source, the WKT can be used for waking up the part from any
low power mode or for general-purpose timing.
23.3 Basic configuration
•
In the SYSAHBCLKCTRL register, set bit 9 (
) to enable the clock to the
register interface.
•
Clear the WKT reset using the PRESETCTRL register (
).
•
The WKT interrupt is connected to interrupt #15 in the NVIC. See
•
Enable the low power oscillator in the PMU (
•
Enable the FRO and FRO output in the PDRUNCFG register if used as the clock
source for the timer (
).
•
To use an external clock source for the self-wake-up timer, enable the clock input for
pin PIO0_28 in the DPDCRTL register (
) and enable the external clock
option in the self-wake-up timer CTRL register (see
). The external clock
source can be used in all power modes including deep power-down mode.
•
Disable the external clock input in the DPDCTRL register to minimize power
consumption if not using the external clock source option. See
•
Disable the WAKEUP function in the DPDCTRL register to minimize power
consumption if the part does not need to wake up from deep power-down mode via a
pin. See
•
See
to enable the various power down modes.
UM11029
Chapter 23: LPC84x Self-wake-up timer (WKT)
Rev. 1.0 — 16 June 2017
User manual
