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UM10800 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2016. All rights reserved.
User manual Rev. 1.2 — 5 October 2016 306 of 487
18.1 How to read this chapter
The self-wake-up timer is available on all LPC82x parts.
18.2 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 IRC, 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 IRC 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.
18.3 Basic configuration
•
In the SYSAHBCLKCTRL register, set bit 9 ( Table 35 ) to enable the clock to the
register interface.
•
Clear the WKT reset using the PRESETCTRL register ( Table 23 ).
•
The WKT interrupt is connected to interrupt #15 in the NVIC. See Table 5 .
•
Enable the low power oscillator in the PMU ( Table 63 ).
•
Enable the IRC and IRC output in the PDRUNCFG register if used as the clock source
for the timer (
Table 54 ).
•
To use an external clock source for the self-wake-up timer, enable the clock input for
pin PIO0_28 in the DPDCRTL register (
Table 63 ) and enable the external clock option
in the self-wake-up timer CTRL register (see Table 261 ). 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
Table 63 .
•
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
Table 63 .
•
See Section 6.7.1 to enable the various power down modes.
UM10800
Chapter 18: LPC82x Self-wake-up timer (WKT)
Rev. 1.2 — 5 October 2016 User manual