Continuous Analog Output Operations - Measurement Computing Data Translation DT9857 User Manual

Continuous Analog Output Operations

Use continuously paced analog output mode to output buffered values to the analog output
channels and/or the digital output port continuously at a specified clock frequency. The
DT9857 and DT9857E modules support the ability to start continuous analog output
operations and continuous analog input operations simultaneously.
Note: If you are using the DataAcq SDK, you must specify the data in a particular order. For
example, if your output channel list contains analog output channels 0 and 1 and the digital
output port (channel 2), specify the values in the output buffer as follows: the first output
value for analog output channel 0, the first output value for analog output channel 1, the first
value for the digital output port (channel 2), the second output value for analog output
channel 0, the second output value for analog output channel 1, the second value for the
digital output port (channel 2), and so on.
This is not required in the DT-Open Layers for .NET Class Library.
When it detects a trigger, the module starts writing the values from the output buffer to the
channels specified in the output channel list at the specified clock frequency. The operation
repeats continuously until all the data is output from the buffers or you stop the operation.
Note: Make sure that the host computer transfers data to the output channel list fast enough
so that the list does not empty completely; otherwise, an underrun error results.
To select continuously paced analog output mode, use software to specify the following
parameters:
• Specify the data flow as Continuous.
• Specify WrapSingleBuffer as False to use multiple buffers.
• Specify the D/A output frequency. Refer to
• Specify the trigger source as any of the supported output trigger sources. Refer to
for more information about the supported output trigger sources.
• To start the analog input and analog output operations simultaneously using the DT-Open
Layers for .NET Class Library, use the SimultaneousStart.AddSubsystem,
SimultaneousStart.PreStart, and SimultaneousStart.Start methods. Refer to the
documentation for the DT-Open Layers for .NET Class Library for more information.
We recommend that you allocate a minimum of two buffers for a continuously paced analog
output operation. Data is written from multiple output buffers continuously; when no more
buffers of data are available, the operation stops. The data is gap-free.
page 84 for more information.
Principles of Operation
page 88
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