Data Translation DT9800 Series, User Manual

Page: 44 / 162

Chapter 2
32
When the retrigger occurs, the module scans the channel-gain list
once, then waits for another external retrigger to occur. The process
repeats continuously until either the allocated buffers are filled (if
buffer wrap mode is none) or until you stop the operation (if buffer
wrap mode is single or multiple); refer to
page 36 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 23 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 module ignores external triggers that occur
while it is acquiring data. Only external retrigger events that occur
when the module 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;
• The triggered scan mode usage as enabled;
• The retrigger mode as an external retrigger (retrigger extra for
DataAcq SDK users);
• The number of times to scan per trigger or retrigger (also called
the multiscan count) to 1; and
• The retrigger source as the external trigger (external for DataAcq
SDK users).
Note: For DataAcq SDK users, if you want to use the same trigger
source as both the initial trigger and the retrigger source, specify the
external trigger as the initial trigger source and specify the retrigger
mode as scan-per-trigger. In this case, you need not specify the
retrigger source; the module uses the initial trigger source as the
retrigger source.