Data Translation DT9800 Series, User Manual

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Principles of Operation
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External A/D Sample Clock
An external A/D sample clock is useful when you want to pace
acquisitions at rates not available with the internal A/D sample clock
or when you want to pace at uneven intervals.
Connect an external A/D sample clock to screw terminal TB25 on the
DT9800 Series function module (pin 25 on connector J1). Conversions
start on the rising edge of the external A/D sample clock input signal.
Using software, specify the clock source as external. For DT9800
Series function modules, the clock frequency is always equal to the
frequency of the external A/D sample clock input signal that you
connect to the module through the screw terminal panel.
Triggers
A trigger is an event that occurs based on a specified set of
conditions. The DT9800 Series function module supports the
following trigger sources:
• Software trigger
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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 event occurs when
the DT9800 Series module detects a rising edge on the Ext A/D
Trigger input signal connected to screw terminal TB24 on the
DT9800 Series module (pin 24 of connector J1). The trigger signal
is TTL-compatible. Using software, specify the trigger source as a
external digital trigger (external for DataAcq SDK users).