User manual

Programmer’s Guide Page 61 of 66
AcqrsD1_stopAcquisition. This mode is available in all digitizers except the U1071A-FAMILY and the 10-bit-
FAMILY.
This mode is useful when only the last N out of many occurrences of a signal are of interest. E.g. if you search for a
rare event out of many occurrences, and you only can determine its interest after the event has occurred, then the
„Sequence Wrap‟ mode is applicable.
While this mode even „works‟ for nbrSegments = 1, in practice the value of nbrSegments should be at least 3. It is
important to note that after the acquisition of a segment, the digitizer automatically advances to the next memory
section and immediately (with a dead time of ~ 1 μs) starts recording into it. Thus, usually the very last memory
segment used will necessarily contain uninteresting data, since it will not be stopped with a trigger, but be terminated
with the software command AcqrsD1_stopAcquisition.
Use this code to use the „Sequence Wrap‟ mode:
AcqrsD1_configXXX(.. ); // configure other parameters
AcqrsD1_configMode(instrID, 0, 0, 2);
AcqrsD1_acquire(instrID);
..
AcqrsD1_stopAcquisition(instrID);
The time at which the sequence is terminated with the function AcqrsD1_stopAcquisition depends on an external
event, e.g. operator intervention.
When reading the segments, the segment number should take on the values 0,…(nbrSegments-1). They correspond
to the memory section numbers in the digitizer, not the time order of the acquired segments.
Example: if nbrSegments = 8, the time order of the acquired segments might be (depending on when the sequence
was stopped) 5, 6, 7, 0, 1, 2, 3, 4. Here, the „oldest good‟ segment is the 5
th
segment, followed by the 6
th
, 7
th
, 8
th
, 1
st
etc. The „youngest‟ useful segment is the 2
nd
one, while the 3
rd
or 4
th
segment corresponds to the segment that was
being recorded when the stop-command was received. The 4
th
segment (in this example) usually does not contain any
useful data. However, depending on the timing of the triggers with respect to the acquisition stop it could be that the
3
rd
segment has the corrupted data and the 4
th
is valid.
3.20. Readout of Battery Backed-up Memories
Acqiris digitizers with the battery back-up option permit retaining acquired waveforms during periods of time when
the power might be interrupted.
3.20.1. Preparations before Power-Off
A digitizer only remembers the digitized data array, but not all of the parameters that are needed to interpret the
waveform. These parameters are normally retained in the driver, but are typically lost when power is lost or when the
controlling application is terminated.
It is therefore necessary for the application to transfer the relevant parameters before power-off, typically to a disk,
in such a way that they are again available when restarting the application after power is restored. The following
parameters must be transferred to persistent storage, for each instrument:
Parameters of AcqrsD1_configHorizontal, i.e. sampling interval and delay
Parameters of AcqrsD1_configMemory, i.e. number of samples and number of segments
Parameters of AcqrsD1_configVertical, i.e. Full Scale and offset (the coupling is not relevant!), for each
channel of interest
Two calibrated delay parameters, as obtained with the function calls
Double delayOffset, delayScale;
Acqrs_getInstrumentInfo(ID, "DelayOffset", &delayOffset);
Acqrs_getInstrumentInfo(ID, "DelayScale", &delayScale);
The functions Acqrs_getInstrumentInfo should be called just before the start of the acquisition, i.e. before calling
AcqrsD1_acquire, but after all AcqrsD1_config… functions.
3.20.2. Recovery after Power-Off
In order to read a battery backed-up waveform, you need to execute a special sequence of initialization functions
1. Initialize the digitizer with the following function call: