Data Translation DT3000 Series, User Manual, Page: 77 / 156

Chapter 6
76
Figure 21: Software-Retriggered Scan Mode
Externally-Retriggered Scan Mode
Use externally-retriggered scan mode if you want to accurately control the period between
conversions of individual channels and retrigger the scan based on an external event.
When it detects the initial trigger, the board scans the channel list once, then waits for the
external retrigger to occur. On DT3000 Series boards, the initial trigger and the retrigger
source must be an external digital TTL trigger (TB6 on the DT730 and DT730-T screw terminal
or pin 6 of connector J1 on the DT3000 Series board).
When the retrigger occurs, the board scans the channel list once, then waits for another
external retrigger to occur. The process repeats continuously until either the allocated buffers
are filled or you stop the operation; refer to
page 77 for more information on buffers.
The conversion rate of each channel is determined by the frequency of the A/D sample clock;
refer to
page 71 for more information on the A/D sample clock. The conversion rate of each
scan is determined by the period between external retriggers; therefore, it cannot be accurately
controlled. The board ignores external triggers that occur while it is acquiring data. Only
external retrigger events that occur when the board is waiting for a retrigger are detected and
acted on.
To select externally retriggered scan mode, use software to specify the following parameters:
• The dataflow as Continuous.
• Triggered scan mode as enabled.
• The retrigger mode as an external retrigger.
• The number of times to scan per trigger or retrigger (also called the multiscan count) as 1.
• The initial trigger source as the external digital (TTL) trigger.
Trigger occurs;
channel list scanned
once.
Chan 0
Chan 1
Chan 2
A/D
Sample
Clock
Chan 0
Chan 1
Chan 2 Chan 0
Retrigger occurs;
channel list scanned
once.
Board waits for the
duration of the
retrigger frequency.
Board waits for the
duration of the
retrigger frequency.
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