Chapter 2
Using Your NI 653X
2-30
ni.com
Deciding How to Start and Stop Data Transfer—Triggering
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 can use a hardware trigger to start, stop, or start and stop data
transfer.
The three types of trigger signals available are the start trigger, the stop
trigger, or the start and stop trigger.
Start Trigger
A start trigger is a trigger that initiates a pattern I/O upon receipt of a
hardware trigger on the ACK (STARTTRIG) pin.
Figure 2-16.
Starting Data Transfer Using a Trigger
Stop Trigger
When using a stop trigger, transfer starts upon a software command. Once
a hardware trigger is received on the STOPTRIG pin, a predetermined
amount of pretrigger and posttrigger data is saved in the buffer. Once this
data is in the buffer, transfer stops. If the stop trigger arrives before all the
pretrigger data is acquired, an error is returned in software.
Figure 2-17.
Stopping Data Transfer Using a Trigger
REQ
ACK (STARTTRIG)
Posttrigger Data
REQ
STOPTRIG
Pretrigger Data
Posttrigger Data
