Data Translation DT9816 Series, Руководство пользователя

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Chapter 5
62
Single-Value Operations
Single-value operations are the simplest to use. Using software, you specify the range, gain,
and analog input channel. The module acquires the data from the specified channel and
returns the data immediately. For a single-value operation, you cannot specify a clock source,
trigger source, scan mode, or buffer.
Single-value operations stop automatically when finished; you cannot stop a single-value
operation.
Continuous Scan Mode
Use continuous scan mode if you want to accurately control the period between successive
simultaneous conversions of all channels in a channel list.
When it receives an initial trigger, the module cycles through the channel list, acquiring and
converting the data for each entry in the list (this process is defined as the scan). The module
then wraps to the start of the channel list and repeats the process continuously until either all
the allocated buffers on the subsystem queue are filled or until you stop the operation. Refer to
page 63 for more information about buffers.
The conversion rate is determined by the frequency of the internal sample clock; refer to page
60 for more information about the internal sample clock. The sample rate, which is the rate at
which a single entry in the channel list is sampled, is the same as the conversion rate due to
the simultaneous nature of the module.
To select continuous scan mode, use software to specify the data flow as Continuous.
Figure 17 illustrates continuous scan mode using a channel list with three entries: channel 0,
channel 1, and channel 2. In this example, analog input data is acquired simultaneously on all
channels on each clock pulse of the input sample clock. Data is acquired continuously.
Figure 17: Continuous Scan Mode
Software trigger occurs
Chan 0
Chan 1
Chan 2
Internal
Sample
Clock
Data is acquired continuously
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2
Chan 0
Chan 1
Chan 2