Contec ADA16-32/2(PCI)F, Руководство пользователя

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4. Functions
ADA16-32/2(PCI)F
53
- Data acquisition in ring format
When ring memory is used, data is read always with respect to the current input data write position.
The following sketch shows an image of data acquisition in ring format.
The sampling count obtained is always the number of times of sampling for up to the latest data
(shaded portion below).
The larger the number of samples taken, the older the data item acquired first.
As the ring memory retains data even after that data is acquired, you can fetch the same data any
number of times.
When using a user buffer, the conversion data is transferred directly to application memory by the
driver.
The figure above shows how data is transferred to the user buffer for the case when two channels (0ch
and 1ch) are used. Data transfer uses a single 4 byte packet which is the minimum data transfer size.
Each packet contains two AD conversion data values in binary format.
In the above example, the lower two bytes of the packet contain the channel 0 data and the upper two
bytes contain the channel 1 data.
When using two channels, each packet (each data transfer) contains the data for one sampling.