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Chapter 5
Set to About-Trigger Acquisition Mode
The sample clock source and sample rate
The trigger source and edge type
The total acquired sample number N
The specific sample number M before the trigger event. The range
of preset sample number is 2 samples minimum and is limited on
basis of memory size of your host PC.
In about-trigger mode, users must first designate the size of the
allocated memory and the amount of samples to be snatched after the
trigger event happens. The about-trigger acquisition starts when the
first clock signal comes in. Once a trigger event happens, the on-going
data acquisition will continue until the designated amount of samples
have been reached. When the PCI-1712/1712L detects the selected
about-trigger event, the card keeps acquiring the preset number of
samples, and kept the total number of samples on the FIFO.
1
Pre-Trigger Acquisition Mode
Pre-Trigger mode is a particular application of about-trigger mode. Use
pre-trigger acquisition mode when you want to acquire data before a
specific trigger event occurs. Pre-trigger acquisition starts when you
start the operation and stops when the trigger event happens. Then
the specific number of samples will be reversed in the FIFO before the
pre-trigger event occurred. Please specify the following parameters,
when using software in Pre-trigger acquisition mode:
Set to Pre-Trigger Acquisition Mode
The sample clock source and sample rate
The trigger source and gate type
Assume the total acquired sample number is N, then set the total
sample number to be N+2.
PCI-1712/1712L User's Manual
Trigger Event
N-M
2
3
Total Acquired sample number: N
Figure 5-3: About-Trigger Acquisition Mode
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Acquired number of
samples M after trigger
event happened
N
t
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