Data Format And Transfer; Error Conditions - Measurement Computing Data Translation DT9857 User Manual

Data Format and Transfer

DT9857 and DT9857E modules use offset binary data encoding, where 000000 represents
negative full-scale, and FFFFFFh represents positive full-scale. Use software to specify the
data encoding as binary. The ADC outputs FFFFFFh for above-range signals, and 000000 for
below-range signals.
Before you begin acquiring data, you must allocate buffers to hold the data. A Buffer Done
event is returned whenever a buffer is filled. This allows you to move and/or process the data
as needed.
We recommend that you allocate a minimum of two buffers for continuous analog input
operations. Data is written to multiple allocated input buffers continuously; when no more
empty buffers are available, the operation stops. The data is gap-free.
Note: DT9857 and DT9857E modules have a 16 kSample input FIFO that is used to store the
acquired data before it is sent to the host.

Error Conditions

DT9857 and DT9857E modules report any overrun errors by sending an overrun event to the
application program. This event indicates that data buffers are not being sent from the module
to the host fast enough, and the A/D converter ran out of buffers. To avoid this error, try one
or more of the following:
• Reduce the clock rate of the A/D
• Increase the size of the buffers
• Increase the number of buffers
• Close any other applications that are running
• Run the program on a faster computer
If one of these error conditions occurs, the module stops acquiring and transferring data to the
host computer.
Principles of Operation
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