Datapixx(‘SetAdcSchedule’, scheduleOnset, scheduleRate, maxScheduleFrames [, channelList=0] [, bufferBaseAddress=4e6] [, numBufferFrames=maxScheduleFrames]);
Configure a schedule for autonomous ADC analog signal acquisition.
-“scheduleOnset” is the desired delay (in double precision seconds) between
schedule initiation, and the first ADC sample acquisition.
-“scheduleRate” is the rate at which the ADC’s acquire successive samples.
scheduleRate has two formats. It can be a single number, or a 2 element array.
If it is a single number, then it specifies integer samples/second. If it is a 2
element array, then the first element specifies the rate, and the second element
specifies the units of the rate.
If units = 1, then the rate is interpreted as integer samples/second.
If units = 2, then the rate is interpreted as integer samples/video frame.
If units = 3, then the rate is interpreted as double precision seconds/sample
Regardless of the actual format chosen, the resulting sample rate cannot exceed
-“maxScheduleFrames” has two modes, depending on whether the acquisition dataset
has a fixed known length. If the dataset length is known (eg: 100000 samples),
then just pass 100000 to maxScheduleFrames. In this mode, once the ADC
acquisition schedule is started with StartAdcSchedule, the schedule will
terminate automatically when maxScheduleFrames has been acquired. If the dataset
length is not known in advance, then pass 0 to maxScheduleFrames. In this mode,
the acquisition will continue until the schedule is manually stopped using
-“channelList” is a 2D matrix of the ADC channels which should be saved to the
acquisition buffer, and the differential voltage references which should be used
for each voltage acquired. The first row of the matrix contains 1 or more
integers in the range 0 to GetAdcNumChannels-1. This is the list of ADC channels
which will be acquired. The second row of the matrix indicates the differential
voltage references for each acquired channel. The reference is selected using a
code in the range 0-3. Code 0 is used when no differential subtraction is
required during acquisition. All analog inputs are referenced to ground, also
known as single-ended acquisition. Code 1 implements fully differential inputs,
subtracting the adjacent channel’s voltage before acquiring (eg: acquiring ADC0
with code = 1 would subtract the ADC1 voltage from the ADC0 voltage, writing the
result to the acquisition buffer). When using this mode, data is typically
acquired only on the even channels, effectively halving the number of available
channels. Code 2 implements a differential input referenced to the REF0 analog
input (see the Datapixx user manual for pinouts). This has the benefits of
high-impedance differential inputs, without having to sacrifice half of the
channels as with fully differential inputs. Code 3 implements a differential
input referenced to the REF1 analog input. It is possible to use different codes
for different analog channels in a single acquisition schedule. For example ADC0
and ADC1 could be acquired single-ended while ADC2 is referenced to ADC3, and
ADC4/5/6/7 could be referenced to REF0. It is also possible to pass only a
single row of ADC channels to channelList. In this case, all of the ADC channels
will be acquired single-ended.
-“bufferBaseAddress” specifies the start of the RAM buffer which should hold the
acquired data inside the Datapixx. Use ReadAdcBuffer to upload the acquired data
from this address after calling StartAdcSchedule.
-“numBufferFrames” specifies the desired size of the acquisition buffer in the
Datapixx RAM. For many applications, the Datapixx has enough RAM to acquire a
complete dataset without streaming. In these cases, numBufferFrames could be
left at its default value of maxScheduleFrames. The Datapixx typically has 128
MB of internal RAM which is shared between all I/O subsystems (DAC/ADC/AUDIO,
etc). Datapixx(‘GetRamSize’) can be used to query the quantity of RAM in your
system. If maxScheduleFrames is larger than numBufferFrames (or 0), then each
time the acquisition frame counter reaches a multiple of numBufferFrames, the
acquisition buffer address automatically wraps back to bufferBaseAddress. This
circular buffer effect can be used for acquiring arbitrarily long analog
datasets. Simply monitor newBufferFrames returned by GetAdcStatus, and use
ReadAdcBuffer in streaming mode to upload newly acquired data from the Datapixx
RAM to the host.
Note that every call to StartAdcSchedule must be preceeded by a call to
SetAdcSchedule (ie: multiple calls to StartAdcSchedule each require their own
call to SetAdcSchedule)).
Note that schedule timing is implemented in hardware with microsecond precision.
See DatapixxAdc*Demo files for examples.