User`s manual

Continuous Data Transfer 83
PCIS-DASK
Trigger Mode Data Acquisition for Analog Input
5.3 Trigger Mode Data Acquisition for Analog Input
A trigger is an event that occurs based on a specified set of condi-
tions. An interrupt mode or DMA-mode analog input operation can
use a trigger to determinate when acquisition stops or starts.
The PCIS-DASK also provides two buffering methods for trigger
mode AI double-buffering and single-buffering. However, the sin-
gle buffer in trigger mode AI is different from that in non-trigger
mode AI. It is a circular buffer just like that in double buffer mode
but the data stored in the buffer can be processed only when the
continuous data reading is completed. The buffer is reused until
the data acquisition operation is completed. Therefore, to keep the
data you want to transfer from being overwritten, the size of the
single buffer should be the same as or larger than the amount of
data you want to access.
For example, if you want to perform single-buffered middle-trigger
AI with PCI-9812, and the amount of data you want to collect
before and after the trigger event are 1000 and 3000, respectively,
the size of single buffer should be at least 4000. Since the data are
handled after the input operation is completed, data loss problems
are eliminated.
Since PCIS-DASK uses asynchronous AI to perform trigger mode
data acquisition, the SyncMode of continuous AI should be set as
ASYNCH_OP.