UM11029
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© NXP Semiconductors N.V. 2017. All rights reserved.
User manual
Rev. 1.0 — 16 June 2017
447 of 515
NXP Semiconductors
UM11029
Chapter 26: LPC84x 12-bit Analog-to-Digital Converter (ADC)
Table 444. A/D Conversion Sequence A Control Register (SEQA_CTRL, address 0x4001 C008) bit description
Bit
Symbol
Value
Description
Reset
value
11:0
CHANNELS
Selects which one or more of the twelve channels will be sampled and
converted when this sequence is launched. A 1 in any bit of this field will
cause the corresponding channel to be included in the conversion sequence,
where bit 0 corresponds to channel 0, bit 1 to channel 1 and so forth.
When this conversion sequence is triggered, either by a hardware trigger or
via software command, A/D conversions will be performed on each enabled
channel, in sequence, beginning with the lowest-ordered channel.
Remark:
This field can ONLY be changed while the SEQA_ENA bit (bit 31)
is LOW. It is allowed to change this field and set bit 31 in the same write.
0x00
14:12
TRIGGER
Selects which of the available hardware trigger sources will cause this
conversion sequence to be initiated. Program the trigger input number in this
field.
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.
0x0
17:15
-
Reserved.
-
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 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