National Instruments 653X - page 39

Chapter 2 Using Your 653X
© National Instruments Corporation 2-21 653X User Manual
•The polarity (whether to trigger on data that matches or mismatches
the specified pattern)
For example, if you want to start acquisition when the two least significant
bits of your data are 1 and 0, you would specify your trigger parameters to
match those in Figure 2-11.
Figure 2-11. Pattern-Matching Trigger Example
Tip To prevent a transient data value during line switching from falsely causing a match,
set a valid pattern for at least 60ns to guarantee detection. In addition, keep glitches to less
than 20 ns to guarantee rejection.
Choosing Continuous or Finite Data Transfer
You can transfer data continuously into or from computer memory or
specify the number of points you want to transfer.
Finite Transfers
For finite transfers, the 653Xdevice transfers the specified amount of data
to/from computer memory and stops the operation.
Continuous Input
For continuous input, the 653Xdevice transfers input data to the computer
memory buffer continuously. As the device is filling the buffer, call the
DIG_DB_Transfer function or the DIO Read VI to retrieve the data. If at
any time the device runs out of space in the buffer, it stops the operation
and NI-DAQ returns an error.
You have the option to allow the device to continue when it runs out of
buffer space and overwrite data you have not yet read. You can specify this
through the oldDataStop parameter in the DIG_DB_Config function and
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Postive: Search for Match
Pattern to Detect
Mask
Polarity