UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
426 of 515
NXP Semiconductors
UM11029
Chapter 23: LPC84x Self-wake-up timer (WKT)
23.6.2 Count register
Do not write to this register while the counting is in progress.
Remark:
In general, reading the timer state is not recommended. There is no mechanism
to ensure that some bits of this register don't change while a read is in progress if the read
happens to coincide with an self-wake-up timer clock edge. If you must read this value, it
is recommended to read it twice in succession.
1
ALARMFLAG
Wake-up or alarm timer flag.
-
0
No time-out. The self-wake-up timer has not timed out. Writing a 0 to has no
effect.
1
Time-out. The self-wake-up timer has timed out. This flag generates an interrupt
request which can wake up the part from any reduced power mode including
Deep power-down if the clock source is the low power oscillator. Writing a 1 clears
this status bit.
2
CLEARCTR
Clears the self-wake-up timer.
0
0
No effect. Reading this bit always returns 0.
1
Clear the counter. Counting is halted until a new count value is loaded.
3
SEL_EXTCLK
Select external or internal clock source for the self-wake-up timer. The internal
clock source is selected by the CLKSEL bit in this register if SET_EXTCLK is set
to internal.
0
0
Internal. The clock source is the internal clock selected by the CLKSEL bit.
1
External. The self-wake-up timer uses the external WKTCLKIN pin.
31:4
-
Reserved.
-
Table 424. Control register (CTRL, address 0x4000 8000) bit description
Bit
Symbol
Value
Description
Reset
value
Table 425. Counter register (COUNT, address 0x4000 800C) bit description
Bit
Symbol
Description
Reset
value
31:0
VALUE
A write to this register pre-loads start count value into the timer
and starts the count-down sequence.
A read reflects the current value of the timer.
-
