Data Translation DT9857, Руководство пользователя, Страница: 86 / 192

Chapter 5
86
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.
The waveform pattern size must be the same for all output channels, and the total number of
samples must be a multiple of the total number of output channels.
If the waveform pattern is equal to or less than the size of the output FIFO on the module, the
host computer transfers the entire waveform pattern to the output FIFO. When it detects a
trigger, the module starts writing output values to the output channels, as determined by the
output channel list, at the specified clock rate. The channels are updated simulataneously. The
module recycles the data, allowing you to output the same pattern continuously without any
further CPU or USB bus activity. When it reaches the end of the FIFO, the module returns to
the first location of the FIFO and continues outputting the data. This process continues
indefinitely until you stop it.
If the waveform pattern is greater than the size of the output FIFO, the buffer resides on the
host computer. When it detects a software trigger, the module starts writing output values to
the output channels, as determined by the output channel list, at the specified clock rate using
CPU and USB bus intervention. The driver manages the buffer, allowing you to output the
same pattern continuously. When it reaches the end of the buffer, the software returns to the
first location of the buffer and continues outputting the data. This process continues
indefinitely until you stop it.
To select waveform generation mode, use software to specify the following parameters:
• Specify the data flow as Continuous
• Specify WrapSingleBuffer as True to use a single buffer
• Specify the clock source as internal and specify the clock frequency. Refer to page 84 for
more information about the clock source and frequency.
• Specify the trigger source as any of the supported output trigger sources. Refer to page 88
for more information about the supported output trigger sources.
The DT9857 and DT9857E hardware supports the ability to mute the output voltage to 0 V.
Muting the output does not stop the analog output operation; instead, the analog output
voltage is reduced to 0 V over 1020 samples. When desired, you can use unmute the output
voltage to its current level. Refer to your software documentation for more information on
muting and unmuting the output voltage.