Measurement Computing Data Translation DT3034, User Manual

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Principles of Operation
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To select externally-retriggered scan mode, use software to specify the following parameters:
• The dataflow as Continuous.
• Triggered scan mode as enabled.
• The retrigger source as an external digital (TTL) trigger.
• The number of times to scan per trigger or retrigger (also called the multiscan count).
Note:
If you are using an external trigger source as the initial trigger and want to retrigger
externally, specify the same trigger source as the retrigger. For example, if you are using an
external digital (TTL) trigger as the initial trigger, specify the external digital (TTL) trigger as
the retrigger.
An A/D Trigger Out signal is provided for your use. This signal is high when the A/D
subsystem is waiting for a trigger and low when a trigger occurs. In externally-retriggered
scan mode, this signal stays goes low when the trigger occurs and stays low until the desired
number of samples have been acquired, then goes high until the external retrigger is
generated.
Triggers
A trigger is an event that occurs based on a specified set of conditions. DT3034 boards support
a number of trigger sources and trigger acquisition modes, described in the following
subsections.
Trigger Sources
DT3034 boards support the following trigger sources:
• Software trigger
• External digital (TTL) trigger
• Analog threshold trigger
This subsection describes these trigger sources in more detail.
Software Trigger
A software trigger event occurs when you start the analog input operation (the computer
issues a write to the board to begin conversions). Specify the software trigger source in
software.