UM10462
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User manual
Rev. 5.5 — 21 December 2016
46 of 523
NXP Semiconductors
UM10462
Chapter 3: LPC11U3x/2x/1x System control block
3.7 Start-up behavior
See
for the start-up timing after reset. The IRC is the default clock at Reset and
provides a clean system clock shortly after the supply voltage reaches the threshold value
of 1.8 V.
3.8 Brown-out detection
The LPC11U3x/2x/1x includes up to four levels for monitoring the voltage on the V
DD
pin.
If this voltage falls below one of the selected levels, the BOD asserts an interrupt signal to
the NVIC or issues a reset, depending on the value of the BODRSTENA bit in the BOD
control register (
The interrupt signal can be enabled for interrupt in the Interrupt Enable Register in the
NVIC (see
) in order to cause a CPU interrupt; if not, software can monitor the
signal by reading a dedicated status register.
If the BOD interrupt is enabled in the STARTERP1 register (see
) and in the
NVIC, the BOD interrupt can wake up the chip from Deep-sleep and power-down mode.
If the BOD reset is enabled, the forced BOD reset can wake up the chip from Deep-sleep
or Power-down mode.
Fig 8.
Start-up timing
valid threshold
= 1.8V
processor status
V
DD
IRC status
internal reset
GND
80
μ
s
101
μ
s
boot time
user code
boot code
execution
finishes;
user code starts
IRC
starts
supply ramp-up
time
55
μ
s