Chapter 2 Hardware Overview
NI 5911 User Manual 2-12 ni.com
Trigger Hold-Off
The trigger hold-off is a length of time that the NI 5911 waits after a trigger
is accepted before it accepts another trigger. In other words, when a trigger
is received during acquisition, the trigger counteris loaded with the desired
hold-off time. Hardware then rejects all triggers until the counter has
expired or the current acquisition completes, whichever is longer.
Note
The time the acquisition takes to complete from the time a trigger occurs is
(posttrigger samples)/(sample rate (megahertz)). If this time is larger than the trigger
hold-off time, the trigger hold-off has no effect because triggers are always rejected during
acquisition.
Trigger hold-off is provided in hardware using a 32-bit counter clocked
by a 25 MHz internal timebase. With this configuration, you can select
a hardware hold-off value of 40 ns to 171.8 s in increments of 40 ns.
Figure 2-8 shows a timing diagram of signals when hold-off is enabled
and the hold-off time is longer than posttriggered acquisition.
Figure 2-8. Timing with Hold-Off Enabled
Trigger
Hold-Off
Acquisition
In Progress
Pretrigger
Data
Posttrigger
Data
Hold-OffTime in nanoseconds
(Adjustable between 40 ns and 171.8 s)
= Trigger Not Accepted
= Trigger Accepted
