Acqiris SA240P - Page 32

3.2 Simultaneous acquisition and readout (CST option)
32 Acqiris SA240P User's Manual
Output data streams
Acquired data stream per channel
Acquired samples are in 14-bit format but 32-bit data are streamed on output.
When reading data, each int32 data returned by the function StreamFetchDataInt32 contains
14-bit raw data, mapped on 16-bits and left aligned.
The NbOfElementsToFetch should verify:
NbOfElementsToFetch = NbOfSamplesToFetch / 2
The number of elements to fetch represents a number of data and markers in Int32 format.
For example:
AqMD3_StreamFetchDataInt32(session, "StreamCh1", numElementsToFetch,
elements.size(), elements.data(),&availableElements, &actualElements,
&firstValidElement);
Where:
- StreamCh1/StreamCh2: defines the 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 two 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 96 95 32 31 8 7 0
Reserved for future use Trigger position Trigger index
0x01
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
1
st
sample). If the customer application requires the trigger position at sub-sample, the information is
available on the marker stream (absolute trigger position).
Data truncation
The data truncation is supported with the digitizer acquisition mode only.