Data Translation DT9834 Series, Руководство пользователя

Страница: 92 / 186

Chapter 5
92
Using software, specify the clock source as external. The clock frequency is always equal
to the frequency of the external DAC clock output signal that you connect to the module.
Output Conversion Modes
DT9834 Series modules support the following conversion modes:
• Single-value operations are the simplest to use but offer the least flexibility and efficiency.
Use software to specify the analog output channel that you want to update, and the value
to output from that channel. For a single-value operation, you cannot specify a clock
source, trigger source, or buffer. Single-value operations stop automatically when
finished; you cannot stop a single-value operation.
• Continuous analog output operations take full advantage of the capabilities of the
DT9834 Series modules. In this mode, you can specify an output channel list, clock source,
trigger source, buffer, and buffer wrap mode. Two continuous analog output modes are
supported: continuously paced and waveform generation mode. These modes are
described in the following subsections.
Note that in waveform mode, each channel in the output channel list must write the same
number of values, use the same output clock (refer to
page 91 ), and use the same output
trigger (refer to page 91 ).
Continuously Paced Analog Output
Use continuously paced analog output mode if you want to accurately control the period
between conversions of individual channels in the output channel list (refer to
page 90 for
information on specifying the output channel list).
Use software to fill the output buffer with the values that you want to write to the DACs and
to the digital output port, if applicable. For example, if your output channel list contains only
DAC0 and the digital output port, specify the values in the output buffer as follows: the first
output value for DAC0, the first output value for the digital output port, the second output
value for DAC0, the second output value for the digital output port, and so on.
When it detects a trigger, the module starts writing the values from the output buffer to the
channels specified in the output channel list. The operation repeats continuously until either
all the data is output from the buffers or you stop the operation. Refer to
page 94 for more
information about buffers.
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 trigger source as any of the supported trigger sources. Refer to page 91 for
more information about the supported trigger sources.