A useful feature found in most modern digital oscilloscopes is trigger holdoff, a condition that can be added to edge or pattern triggers. Trigger holdoff enables the user to disable the trigger temporarily, even if the trigger conditions are met, until the holdoff conditions are also met. The trigger fires when the holdoff elapses.
One can also think of trigger holdoff as a function used when there are multiple trigger events in a given acquisition, but you're only interested in certain ones. Rather, it lets users ignore those uninteresting trigger events and stabilize the display as though there were only one trigger event per acquisition.
|Figure 1: Edge trigger with holdoff by time|
In Figure 1, the bold edges on the trigger source indicate that a positive slope has been selected. The broken upward-pointing arrows indicate potential triggers, which would occur if other conditions are met. The bold arrows indicate where the triggers actually occur when the holdoff time has been exceeded.
|Figure 2: Edge trigger with holdoff by events|
In general, holdoff can be used in several different applications:
One can envision many applications in which trigger holdoff might be extremely useful, such as debugging the read channel of a disk drive or memory, where only, say, the pulses initiating a specific sector is of interest and you know how far apart in time such pulses occur.