Data Translation DT9828, User Manual

Page: 64 / 116

Chapter 5
64
Continuous Scan Mode
Continuous scan mode takes full advantage of the capabilities of the DT9828 module. You can
specify a channel list, sampling frequency, start trigger, and buffer using software.
You can enter up to 1024 entries in the channel list. For the DT9828, channels 0 to 7 correspond
to the analog input channels and channel 8 corresponds to the digital input port. Using
software, specify the channels you want to sample.
When a software trigger (software command) is detected, the module cycles through the
channel list, acquiring and converting the value for each entry in the list (this process is
defined as the scan). The sampled data is placed in the allocated buffer(s). When the module
gets to the end of the channel list, it wraps to the start of the channel list and repeats the
process continuously until you stop the operation.
Using software, you can stop a scan by performing either an orderly stop or an abrupt stop. In
an orderly stop, the module finishes acquiring the current buffer, stops all subsequent
acquisition, and transfers the acquired data to host memory; any subsequent triggers are
ignored. In an abrupt stop, the module stops acquiring samples immediately; the current
buffer is not completely filled, it is returned to the application only partially filled, and any
subsequent triggers are ignored.
The conversion rate is determined by the sampling frequency of the input sample clock; refer
to
page 62 for more information about the input sample clock.
To select continuous scan mode, use software to specify the following parameters:
• Specify the data flow as Continuous
• Specify the clock source as internal and specify the sampling frequency (refer to page 62 )
• Specify the trigger as a software trigger (refer to page 63 )
Figure 14 illustrates continuous scan mode with a channel list of three entries: channel 0
through channel 2. In this example, analog input data is acquired when a software trigger is
detected.
Figure 14: Continuous Scan Mode on the DT9828 Module
Chan 1
Input
Sample
Clock
Chan 2 Chan 0 Chan 1
Software Trigger occurs
Data is acquired continuously
Chan 0 Chan 2