National Instruments 653X Manuale Utente

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You need to specify which of the lines in your acquisition you want to 
monitor for changes.

Specify which bits are significant to you by using a software line mask in 
the 

DIG_Trigger_Config

 function in NI-DAQ C interface, and the 

Digital Trigger Config VI for LabVIEW. In the following example, the user 
specifies the mask to detect changes on the two least-significant bits of a 
port. Pattern 1 does not have changes in the two bits of interest and data is 
not latched, but for pattern 2, a change is detected on one of the two bits of 
interest, and the value of the entire port is acquired.

Figure 2-15.  Change Detection Example Settings

By default, data transfer starts upon a software command (the 
Digital Buffer Control VI called by the DIO Start VI in LabVIEW and the 

DIG_Block_In

 and 

DIG_Block_Out

 functions in NI-DAQ C interface). 

However, you have the option of using a hardware trigger to start, stop, or 
start and stop data transfer.

16 bits

Port 0, Port 1

Group 1

Port 2, Port 3

Group 2

32 bits

Port 0, Port 1, Port 2, Port 3

Group 1

Mask

0 0 0 0 0 0 1 1

Initial Input 
Pattern

0 0 0 0 0 0 1 0

Input  Pattern  1

0 1 0 0 0 0 1 0

No change on specified 
bits. 
Data is not latched.

Input  Pattern  2

0 0 0 0 0 0 1 1

Change detected, 
latch entire port.

Table 2-4.  Port and Timing Controller Combinations (Continued)