Data Translation DT9820 Series, User Manual

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Chapter 2
14
Triggers
A trigger is an event that occurs based on a specified set of
conditions. The DT9820 Series function module supports the
following trigger sources:
• Software trigger
−
A software trigger event occurs when you
start the analog input operation (the computer issues a write to
the module to begin conversions). Using software, specify the
trigger source as a software trigger.
• External trigger
−
An external digital trigger occurs when the
DT9820 Series module detects a high-to-low transition on a
digital input line. Depending on the digital input line, the A/D
conversion is either started or paused, as shown in
Table 4 .
When the operation is paused, the driver does not empty the data
buffers; therefore, the buffers contain the data that was acquired
before the operation was paused. When the operation is restarted
(another external trigger of the same type occurs), this data is
emptied and sent to the host application program and the buffers
are refilled with new data.
Using software, specify the trigger source as an external trigger.
Table 4: Triggering A/D Conversions with Digital Input Lines
To Start an A/D
Conversion on
A/D Subsystem..
Need a High-to-Low
Transition on Digital
Input Line...
To Pause or Stop an
A/D Conversion on
A/D Subsystem..
Need a High-to-Low
Transition on
Digital Input Line...
0 0 0 4
1 1 1 5
2 2 2 6
3 3 3 7