Measurement Computing Data Translation DT9857, Руководство пользователя

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Chapter 5
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Once the sample clock is started, the module requires 39 conversions before the first A/D
sample is valid. The valid sample is aligned with the A/D trigger.
Note: The DT9857 and DT9857E modules have two power modes: low power mode and
high power mode. Low power mode is used when you specify a sampling frequency less
than 52.734 kHz. High power mode is used when you specify a sampling frequency greater
than or equal to 52.734 kHz. If you change the power mode from low to high power or from
high power to low power, and then configure the device, the module is self-calibrated. You
may notice that it takes time after the device is configured to complete the calibration process.
Analog Input Conversion Modes
The DT9857 and DT9857E modules support single-value, single-values, and continuous scan
mode to acquire and convert analog input data. This section describes each of these
conversion modes.
Single-Value Operations
Single-value operations are simpler to use than continuous operations. Using software, you
specify the analog input channel and the gain that you want to use. For the DT9857-08 and
DT9857E-08, specify channel 0 to 7; for the DT9857-16 and DT9857E-16, specify channel 0 to
15. The module acquires the data from the specified channel and returns the data immediately.
For single-value operations, you cannot specify a clock frequency, trigger source, scan mode,
or buffer. Single-value operations stop automatically when finished; you cannot stop a
single-value operation.
Single-Values Operations
For the DT9857-08, DT9857E-08, DT9857-16, or DT9857E-16 module, you may prefer to read a
single value from all the analog input channels simultaneously using one software call. This is
called a single-values operation. You specify the analog input subsystem and the gain that you
want to use for the channels (not the channels themselves). The module then acquires a value
from each input channel simultaneously; the data is returned as an array of input values.
For single-values operations, you cannot specify a clock frequency, trigger source, scan mode,
or buffer. Single-values operations stop automatically when finished; you cannot stop a
single-values operation.
Note: Data is returned from the analog input channels only.