UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
450 of 515
NXP Semiconductors
UM11029
Chapter 26: LPC84x 12-bit Analog-to-Digital Converter (ADC)
18
TRIGPOL
Select the polarity of the selected input trigger for this conversion
sequence.
Remark:
In order to avoid generating a spurious trigger, it is
recommended writing to this field only when the SEQA_ENA bit (bit
31) is low. It is safe to change this field and set bit 31 in the same
write.
0
0
Negative edge. A negative edge launches the conversion sequence
on the selected trigger input.
1
Positive edge. A positive edge launches the conversion sequence
on the selected trigger input.
19
SYNCBYPASS
Setting this bit allows the hardware trigger input to bypass
synchronization flip-flops stages and therefore shorten the time
between the trigger input signal and the start of a conversion. There
are slightly different criteria for whether or not this bit can be set
depending on the clock operating mode:
Synchronous mode: Synchronization may be bypassed (this bit may
be set) if the selected trigger source is already synchronous with the
main system clock (eg. coming from an on-chip, system-clock-based
timer). Whether this bit is set or not, a trigger pulse must be
maintained for at least one system clock period.
Asynchronous mode: Synchronization may be bypassed (this bit
may be set) if it is certain that the duration of a trigger input pulse will
be at least one cycle of the ADC clock (regardless of whether the
trigger comes from and on-chip or off-chip source). If this bit is NOT
set, the trigger pulse must at least be maintained for one system
clock period.
0
0
Enable synchronization. The hardware trigger bypass is not
enabled.
1
Bypass synchronization. The hardware trigger bypass is enabled.
25:20
-
Reserved, user software should not write ones to reserved bits. The
value read from a reserved bit is not defined.
N/A
26
START
Writing a 1 to this field will launch one pass through this conversion
sequence. The behavior will be identical to a sequence triggered by
a hardware trigger. Do not write a 1 to this bit if the BURST bit is set.
Remark:
This bit is only set to a 1 momentarily when written to
launch a conversion sequence. It will consequently always
read-back as a zero.
0
27
BURST
Writing a 1 to this bit will cause this conversion sequence to be
continuously cycled through. Other B triggers will be ignored while
this bit is set.
Repeated conversions can be halted by clearing this bit. The
sequence currently in progress will be completed before
conversions are terminated.
0
Table 445. A/D Conversion Sequence A Control Register (SEQA_CTRL, address 0x4001 C008) bit description
Bit
Symbol
Value
Description
Reset
value