Data Translation DT9800 Series, User Manual

Page: 39 / 162

Principles of Operation
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Continuously Paced Scan Mode
Use continuously paced scan mode if you want to accurately control
the period between conversions of individual channels in a scan.
When it detects an initial trigger, the module cycles through the
channel-gain list, acquiring and converting the value for each entry in
the list (this process is defined as the scan). The module then wraps to
the start of the channel-gain list and repeats the process continuously
until either the allocated buffers are filled or until you stop the
operation. Refer to
page 36 for more information on buffers.
The conversion rate 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 sample rate, which is the rate at which a single
entry in the channel-gain list is sampled, is determined by the
frequency of the A/D sample clock divided by the number of entries
in the channel-gain list.
To select continuously paced scan mode, use software to specify the
dataflow as continuous and to specify a trigger source to start the
operation. Refer to
page 25 for more information on the supported
trigger sources.
Figure 3 illustrates continuously paced scan mode using a
channel-gain list with three entries: channel 0, channel 1, and channel
2. In this example, analog input data is acquired on each clock pulse
of the A/D sample clock. When it reaches the end of the channel-gain
list, the module wraps to the beginning of the channel-gain list and
repeats this process. Data is acquired continuously.