
UM10800
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© NXP Semiconductors N.V. 2016. All rights reserved.
User manual
Rev. 1.2 — 5 October 2016
333 of 487
NXP Semiconductors
UM10800
Chapter 21: 12-bit Analog-to-Digital Converter (ADC)
Table 282. 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 SEQB_ENA bit
(bit 31) is LOW. It is permissible 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.