Data Translation DT9824, Руководство пользователя, Страница: 52 / 102

Chapter 5
52
One sample from each of the enabled input channels is called a scan. In software, you specify
the number of scans that you want to acquire in the input buffer.
You can specify one of the following wrap modes for the input buffer in software:
• Continuous wrap mode – Use this mode if you want the input operation to continue
indefinitely. In this case, when the end of the input buffer is reached, the operation wraps
to the beginning of the input buffer overwriting the oldest scan data with the latest scan
data.
• No wrap mode – Use this mode if you want the input operation to stop automatically
when the number of scans specified has been acquired.
Figure 14 illustrates continuous wrap mode using a channel list with five entries: analog input
channel indices 0, 1, 2, 3, and the digital input data (index 4). In this example, data is acquired
simultaneously on all channels on each clock pulse of the input sample clock. Data is acquired
continuously until all the queued buffers have been filled or you stop the operation.
Figure 14: Continuous Wrap Mode
Data Format
The DT9824 module uses offset binary data encoding for the ±10 V bipolar range.
Note: When the DT9824 is above range, the value FFFFFFh (plus full-scale) is returned.
When the DT9824 module is below range, the value 000000h (minus full-scale) is returned.
Initial trigger event occurs
Chan 0
Chan 1
Chan 2
Input
Sample
Clock
Data is acquired continuously
Chan 3
Chan 0
Chan 1
Chan 2
Chan 3
Chan 0
Chan 1
Chan 2
Chan 3
Chan 0
Chan 1
Chan 2
Chan 3
Chan 4 Chan 4 Chan 4 Chan 4