Data Translation DT9800 Series, User Manual

Page: 43 / 162

Principles of Operation
31
2
2
2
2
2
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2
Max. Retrigger = 1
Frequency
Min. Retrigger Period
For example, if you are using 16 channels in the channel-gain list, and
using an A/D sample clock with a frequency of 50 kHz, set the
maximum retrigger frequency to 3.106 kHz, since
3.106 kHz = 1
16 + 2
µ
s
50 kHz
To select internally retriggered scan mode, use software to specify the
following parameters:
• The dataflow as continuous;
• Triggered scan mode usage as enabled;
• The retrigger mode as internal;
• The number of times to scan per trigger or retrigger (also called
the multiscan count) as 1;
• The frequency of the retrigger clock; and
• The initial trigger source; refer to page 25 for more information
on the supported trigger sources.
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 a DT9800 Series function module detects an initial trigger
(either a software trigger or an external trigger), the module scans the
channel-gain list once, then waits for an external retrigger to occur.
The external retrigger occurs when a rising edge is detected on the
Ext A/D Trigger input screw terminal (TB24) on the module.