Acqiris SA230E User Manual page 40

3.2 Simultaneous acquisition and readout (CST option)
Output data streams
Acquired data stream per channel
Acquired samples are in 14-bit format but 32-bit data are streamed in output.
When reading data, each int32 data returned by the function FetchDataInt32 contains 14-bit raw
data, mapped on 16-bits and left aligned.
The NbOfElementsToFetch should verify:
About the number element to fetch: the element represents a number of Int32 of data or markers. For
example:
AqMD3_StreamFetchDataInt32(session, "StreamCh1", numElementsToFetch,
elements.size(), elements.data(),&availableElements, &actualElements,
&firstValidElement);
Where:
- StreamCh1/StreamCh2: definesthe channel to fetch.
- numElementsToFetch: defines the minimum number of Int32 data to be fetched. It must be a
multiple of 16.
- availableElements: returns the number of Int32 data already acquired and available to be
fetched on-board.
- actualElements: returns the number of Int32 data fetched in the current call. This number is
always <= numElementsToFetch.
- firstValidElement: represents the first valid Int32 element in the returned data buffer. It is
used for data alignment reasons.
- elements: contains the int32 data returned by the function.
When fetching the data stream, each int32 contains 2x 14-bit raw data, mapped on 16-bits and left
aligned. For example: element[0] contains sample_0 and sample_1, element[1] contains
sample_2 and sample_3, etc....
Marker stream (absolute trigger position)
The marker stream contains the trigger time-stamps, encoded in 512 bits, as described below.
511
Reserved for future use
Table 3.1 - Trigger time-stamp fields.
The trigger position in number of samples is given by: Returned Trigger position / 256
The trigger position in seconds is given by: Returned Trigger position / (256 x Sampling rate)
Trigger position
Using raw data output, trigger position is known with the accuracy of a sample (corresponding to the
st
1 sample). If customer application requires trigger position at sub-sample, the information is available
on the marker stream (absolute trigger position).
Acquisition sequence
An example of CST acquisition sequence is illustrated below.
40
NbOfElementsToFetch = NbOfSamplesToFetch / 2
96 95
Trigger position
32 31
Trigger index
Acqiris SA230E User's Manual
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